Definitely Rocket launcher; you don't need accuracy as long as you set up the wall-angle correctly, and with a flying suit any alien below a rocket carrying soldier is a goner. I even use them in UFOs - my style of play is to never reload in a game; last terror mission I had two friendly fire rocket casualties, but it was still worth it. In supply vessels, you can use the rocket launchers to shoot on an angle around the corner to the lifts and clear the lift pad without any line of site. You could waste TUs and elerium on a blaster bomb, but using Blaster launcher doesn't increase firing accuracy. Finally, I use the rocket launcher to clear farmhouses, buildings, jungle trees, and other obstacles. If there is an alien in a farm house there is no better way to flush them out (other than blaster launcher, see above). High explosives delay a turn, and again using them to kill aliens does not increase your snipers' accuracy. I would actually rate the rocket launcher the best weapon in the game; the blaster launcher is a great bail-out weapon but is limited in its use and accuracy-accruing benefits. I usually have about 25% of my squad as rocket launchers, 80% heavy plasma, and the rest miscellaneous (blaster launcher, fodder, medic).