PC is most stable.
Xbox is next.
PS3 is last.
But really as long as you're not playing PS3's version, should be stable enough. Glitches are more prominent in the Xbox version compared to the PC version, but totally playable.
True for the most part; if you have a newer PC with a quad core (or more) CPU and/or Win7 getting it to run smoothly can take some tweaking. Once (if) you do, it's smooth sailing.
The 360 version froze up maybe 3-4 times in over 300 hours of gameplay for me. It was very stable, maintaining a good frame rate with rare exception.
PS3 froze up on me 1-2 times for every 10 hours I played (rough estimate). It was very playable, but if you have a choice, don't choose PS3 (for any BGS game, really).