I think a distinction really needs to be made here.
How you play in a sim, and how everything goes, really depends on the medium used.
Play-by-email simming works differently from play-by-post (forum) simming, and both of which work extremely differently compared to IRC simming, which in my humble opinion shares more with MUSHes and MOOs than with either PBEM or PBP simming.
From my own experience, PBEM and PBP are not equivalent. PBP lends itself more to short posts and a much higher pace than PBEM; in PBEM, most sims I've played on use a mix of solo posts and joint posts, versus the tag structure of PBP simming. PBEM posts tend to be longer, besides.
Play by chat, on the other yhand, is way more like MUSHes and MOOs. I've not done play by chat in years, but I still am an active player on MUSHes and MOOs. Biggest hurdle I've found? Those require a time commitment. Because they work in real-time, you can't get by with just a few minutes a day reading posts plus some more time over a week doing your posts, like you can on a PBEM game.
On the other hand, MUSHes and MOOs, if you *can* find the time, have the most impactful roleplay I've ever had. Whether it be a 12-year-old character (on an Ender's Game MOO) discovering girls, or other (older) characters (in other settings) in diplomatic negotiations, or even in combat...It's real-time, so you get a lot more into it. RP in a real-time format is, not to put too fine a point on it, like baring your psyche to the other person, IMHO. No matter how good you are at keeping in character separate from out of character, you will feel it if both parties are any good. This leads to OOC trust being kinda key when you play in real-time in my opinion. People you RP with will likely very quickly become OOC friends, even if they play enemies...and sometimes, even if you try to build barriers. I even found my first serious RL relationship because we both played on a MOO, and very quickly got to know each other. We've never met IRL, sadly, but we knew each other to a very deep level, and what we learned through MOOing has helped us stay friends even years after she broke up with me.
Play by post and PBEM, on the other hand...You have to be a good writer in any of these formats to get the most out of it, but for PBP and PBEM you have to be good at longer forms of writing than chat or MUSH/MOO RP. These longer forms can be just as impactful (I have, as a GM, made players in a Shadowrun PBP game nearly vomit IRL, because my description of something was so gory and realistic), but you have to wield written language very well to get the same level of impact. On the other hand, you tend to get much deeper characters and settings from even newbie players with PBEM in particular (play by chat doesn't lend itself as readily to depth; MUSHes and MOOs can do depth to astounding degrees, but only with an investment of time most players aren't willing to make, I've found.). Don't be surprised if you find you know people OOCly a lot less through PBEM/PBP than more real-time mediums though - that's part of the appeal at times, that you bare a lot less of yourself.
A lot of times, my favorite format varies with the setting - each setting for a game melds with different advantages and disadvantages of the medium. For Shadowrun, for example, because it's a pen and paper RPG we're playing online, I like PBP the best. You get a lot of story and characters, and the pace can vary such that, with adaptations, you can get through an adventure in a good time. For the same reasons, though, I shy away from play-by-chat. (There used to be Shadowrun MUSHes, and I loved them, but they all have largely folded over the years.) I prefer PBP over PBEM for Shadowrun because you can more easily separate OOC chatter, dice rolls, etc, from actual In Character RP without as much confusion. For Star Trek in particular though? I've done MUSHes. My "native RP habitat" is a MUSH or MOO, I joke with friends. (The difference between a MUSH and a MOO is code, nothing a player usually worries about, so I use them both here.) The coding of things like a space system, an economy system, etc. that you'll see on many Trek MUSHes can be fun, but I found I didn't have the speed to keep up, despite loving the RP that resulted.
I've also done play by chat - very briefly. It's a taste thing, but I didn't like IRC or similar for roleplay, not in Trek. Dozens of people in the same space got confusing.
PBP (forum-based RP) can work - I haven't done this format with Trek in years, though.
PBEM, to me, is ideal for Trek where you have (as most sims do) everybody set on the same ship. You can get very in-depth with characters. Plots take time, but a good sim keeps everybody accountable for being active, and goes through "episodic" plots at a fairly good pace.
Arix, this is where you might find PBEM more to your taste than the STO forums. Generally speaking, GMs stick around. (Players can sometimes be flaky.) If you can accept that most people will post once or twice a week in page-or-so sized posts, then the average plot taking a month to month and a half to run through makes sense. Newbie handling on a PBEM is a lot simpler - It's best to leave them to the GM if you can. While I haven't done Trek PBEM GMing, I've done it for other PBEM setups, and while it's always nice when players help guide the newbies, in the end I always felt (when I was a GM) that it was my responsibility - that, whether or not the players had the time or patience to help, the buck stopped with me on keeping quality up as much as quantity. This was as much a practical thing (because newbie-handling can, just as you experienced, be very draining on a player, where a GM should know to expect it) as philosophical. Sometimes, often actually, doing this meant joining a game had to have more than just "Hi I want to join" as a starting point - most PBEMs have character applications not merely to keep out spammers, but also to make sure everybody (prospective player and GM alike) knows going in what the heck the prospective player is capable of.
Your point about being able to tell the good sims from the bad is very well taken, though. There isn't a way to tell at a glance; at any given time there are hordes of sims, most don't survive past a few months, and more pop up to replace the ones that die out. Word of mouth is your best bet to find a quality sim. For sims that post to the RPG recruitment thread here, see if you can read their archives (generally you can). You can get a good sense of a sim's RP through previous posts to a PBEM or PBP, or logs of a play-by-chat sim (MUSHes and MOOs...Well, I hate to say it, but because the code can be such a big part of a MUSH/MOO experience for a setting like Trek, logs don't usually tell the whole story. You really have to just dive in to a MUSH).
Beyond that, defining a "good" sim comes down to taste a lot of times. I'm not opposed to playing in a sim that's part of a fleet, though the sim I advertised here recently is independent (though it was previously part of a fleet); some people, though, hate the experience and stick to independent sims (which also tend to be smaller). I prefer post-NEM Trek RP in the Prime Universe, or at least RP that's willing to say "we only look at canon up to a certain point"; IMHO, you get more freedom that way, because you're generally "post-canon" and don't have to worry about canon saying something is impossible. (I prefer a flexible adherence to canon; some people like to totally ignore it, others to try to stay within its bounds more faithfully.) Other people prefer TNG-based RP, or TOS, or ENT.
Point is that looking for a sim is uncertain, though, yes. Word of mouth is key. But most key? Spending the time to sit down and actually look into the community of players you intend to join.
