It's situational, but generally I prefer accuracy over power. If I have a choice, I generally don't bother with anything that's less than about 85% accurate, but there are some times when I don't have a choice - sleep moves or Will o' Wisp, for instance. If the pokemon could benefit from those moves, it gets them and I just deal with it. But with things like Fire Blast and Hydro Cannon, to me it's just not worth it. I'll always go with the more accurate versions like Flamethrower and Surf. The way I see it, with the more powerful but less accurate moves, I might get a 120 base power hit, but I might get 0. 95 base power is indeed less than 120, but it's a helluva lot more than 0, so it's worth it.
Beyond that though, other factors generally come into play and it really comes down to the individual move and the individual pokemon. If they need the coverage that badly and no other move will work, I might saddle something with a readily available move like Rock Tomb. Or if it's a terribly powerful move that can't be handled any other way, I'll use it - for instance, Heracross gets Megahorn, but only because it can't learn X Scissor. Scolipede can learn X Scissor, so that's what it gets, even though it can also learn Megahorn. And there are even times that I'll go with both - Scrafty, for instance, gets both High Jump Kick and Drain Punch, since HJK hits so hard, but is not only inaccurate, but has consequences. So Drain Punch is there for when it doesn't need the extra oomph of HJK, and with the bonus that it's a drain move, so it can help to patch it up after an HJK miss.