Definitely a personal choice this once (you don't say ...). I've always been a bit worried about looking like a squaddie on leave - not to mention that should I ever find myself in 'trouble' (touch wood), I wouldn't want to be dressed in DPMs and blending into the scenery - not exactly the best thing for any rescue team or search party! But of course, military kit ain't designed to attract attention ... unless you're wearing temperate DPMs in the desrt, that is.
As for quality, I think the military stuff is getting better all the time, and often has a somewhat unfairly 'bad' reputation. Don't quote me on this, but I'm fairly sure that most 'modern' British Army clobber is produced by the likes of Berghaus et al (not that they're the best by any means, but it's no longer the cheapest bidder that wins military contracts). It did make me laugh to discover that British Army face-paint is now produced by the make-up firm L'Oreal (because you're worth it ... !). True.
And in most cases army kit is A LOT cheaper. My advice is to buy it new, however, as the second hand stuff is often well worn in, and worn out!
Personally - I use a mix. Mainly 'civvy' stuff (eg. bergen, boots, jacket, etc), combined with British Army cooking kit, lightweight trousers (still the best in my opinion) and ... this one's gonna make all you Woodlore knife folks wince ... a British Army jungle survival knife! (yeah, yeah, I hear you - big ol' chunk of metal but it does me proud!).
G
PS: would highly recommend the Swedish firm Haglofs for civvy kit, especially bergens and bivvys (thanks to Viking for the original tip off), British firm Snowsled for jackets (should already be familiar to Ray Mears fans), and Brasher for boots.