I chose one Montblanc rollerball which I thought would be the most frequent pen I'd use, but also made sure to pick a decent fountain pen, a Parker 75 gold/silver cisele. Turns out, that when choosing what pen to wear on any given day, I actually pick out the Parker way more often than the Montblanc rollerball (or indeed, a Montblanc Meisterstuck 149 I got a bit later which always fucking leaks a little).
Just to correct this and not give the 149 a bad review unduly, I should point out that I misremembered the exact model of Meisterstuck I have; it's a 146 (what they called "Le Grand", although it's slightly smaller than the 149... go figure).
Also, the leaking does disappear for a few weeks or so if I flush the pen out fully, so it's probably that some kind of gunk is in the reservoir, rather than the pen itself being at fault. I just flushed it out today, which is how I realised I misremembered the model number!

And now that I think about it--spending the money on a good pen that I will use for years makes sense.
I'll probably wind up saving money in the long run, by not having to replace disposable plastic pens. (I do go through a lot of pens) And I won't be adding those aforementioned disposables to the local landfill.
Hmm, I'm not sure the cost argument is correct; don't forget you have to factor in buying ink bottles occasionally. Not that it's expensive or anything, just that overall, it's likely to more or less cancel out not needing new cheap biros. The environmentally-friendly aspect is certainly true.