For Andorians I always picture our fellow poster Therin of Andor's picture! I've just seen it so many times here it always pops into my head. Klingons and Trill I always picture DS9 era. Tellarites and Romulans are always TOS era. I prefer medium/chunky Riker
For Jem'Hadar, I have to say I always think of ones like Talak'talon (minus the eye-brow ridges), Ometi'klan, Remata'klan, Goron'agar etc., before they started (around the time of the Siege of ARR-558?) gluing those weird white spiky things to their noses, and later their lips... What use could those possibly serve? It looked silly to me... the only place it worked for me at all was (about 39 minutes into Til Death do us Part) the Pilot on Weyoun's ship, I think he was the only one with brown hair... and even that was pushing it...
Yeah, didn't DS9 do alot of big makeup changes in the 5th or 6th season? As for the boney horn things that suddenly appeared on the Jem'Hadar, I've been thinking of them as a way to differentiate the Alphas and the Gammas. Although, I'll admit I'm not sure if that would actually work.
I think they may possibly have been trying to differentiate between individual Jem'Hadar... or else following, I think Moore's explanation of the horns around their faces, I think he said you don't walk into a Jem'Hadar- cuz you'll end up bleeding- so now they seem even more pointy and scary... But they seem silly. Especially those ones over the lips!! You could be right about the AQ vs GQ thing, but none of the Jem'Hadar in the ep that intro'd the AQ soldiers had them (1 Little Ship)... one had ugly yellow head spikes though. I've never gotten over that. (Why did he have a uniform like the GQ elder??) And why are the AQ ones so arrogant? They're like Vorta! Do the Founders never learn??? On that note I prefer the later changes they made to the Founders makeup to the initial appearance... the deep set eyes etc.