Indeed, if you perform poorly enough for the resulting lack of Extends to make a substantial difference, It's a Game Over already anyway, in the literal sense. SA is definitely a good choice, stages are well designed and you'll always be able to squeeze out a lot of Bombs/Power if you know what to do.
For me:
SA - bomb in stage no problem, gets power back anyways as long as it's not in the wrong place (like no enemies on the screen) and not too often. The problem is that you can't bomb through bosses easily (ReimuC aside). Thus, often times Orin and Utsuho become huge brick walls.
UFO - can't bomb many times in stage cuz have to save them, have to use UFO summon to cancel bullets and get resources. The UFO system opens up so many more potential places for infuriating errors. The reward is: boss comes *mashes X* boss defeated (except LFS, which is basically a show stopper and can take away as many resources as possible).
Based on this, I'll suggest SA, at least over UFO, if only for having resources given to you no matter how bad you do. Performing near-perfect UFO routes in stages can be just as frustrating as dealing with Orin and Okuu, but at least for SA you don't have to worry about not getting the 8th or 9th life just because you die somewhere bad.
Take note that PCB gives you
more resources than SA (if you reach 1000 point items), and you can avoid much of the memorization by playing as SakuyaA (ultra spread / ultra homing, plus 4 bombs per life to bomb through
a lot of attacks). It's also got a really easy final attack (normal mode Reflowering - avoid red waves completely by dodging them half way above bottom of screen!!)
