I had a cheap Ridgid ($80) orbital sander and it conked out after two strippers. In terms of performance it seemed to be on par, or maybe a little better, with other orbital sanders I'd used in terms of vibration, noise, and on board dust collection. Sanding was not a task I looked forward to and I wore a respirator to deal with the dust.
When that one died I bought the sander I wanted to get in the first place but couldn't justify at the time, a Mirka Ceros. Very expensive and very awesome. I could not be happier with it and if someone stole it today I'd buy another one tomorrow without hesitation. The small size and light weight make it easy to hold on horizontal or upside down surfaces and gives you much more control. It gets into tighter spaces.
I have it connected to a cheap shop vac for dust collection and it's amazing the amount of dust that's collected. Cedar dust will have my nose running and give me a nagging cough within a couple minutes if I start hand sanding without a mask yet I can sand for 3 hours straight with the Mirka, using no mask or respirator, and have no issues. The shop stays much cleaner and I don't even have to blow the dust off my clothes when I get done.
I didn't think I'd have much use for the variable speed but I've really grown to like that feature. If I want to remove a lot of material I can crank it up and if I'm working with softer or thinner material or an outside curve where it's easy to cut too deep I can turn it down.
It's the quietest, smoothest, and most powerful sander I've used (not that I've used a lot of different ones). Believe it or not I almost look forward to sanding now (except the inside), it's a real pleasure to use. Along with the standard pad I also have a soft pad as well as interface pads (really soft) and I've begun to reach for the orbital when I otherwise would have hand sanded only, like rounding over edges and sanding curved surfaces like shaping the stems or sanding gunwales. I think the size and weight have a lot to do with this as this seems to make it much more controllable.
That's pretty much the only sander I use. I do of course still hand sand at times and I have a belt sander but I use it less and less each build, not once on my current one. The general wisdom is to never use a belt sander on the hull. Things can happen very fast with a belt sander and I believe it's harder to have a delicate touch. Momentum used one to sand the outside of his hull but he has lots of experience using them as a furniture maker.
I wouldn't use something like a high speed grinder. You're working with cedar after all, it sands pretty darn easy. You'd need to finish with an orbital anyway to remove all the scratches.
I start with 40 grit and that removes material plenty fast. I had a hard time finding anything coarser than 60 grit and when I did the quality was very poor. Now I've bought some 40 and 60 grit discs from Industrial Abrasives (
http://www.industrialabrasives.com/) and have been very happy with them.
Alan