Paint Striper which one is best for aluminum?

There is no best one for aluminum. It's the paint you want to strip. Not the aluminum. As far as which is the best paint stripper is concerned, that depends on what kind of paint you are stripping. If it's house paint you will most likely have to sand it off. Because there is not really any good paint stripper out there that does large surface house paint very well. If it's Auto Paint, you will find a few different kinds to choose from. I've used Jasco airplane paint stripper and it seems to work the best. It's still a big hassle and you need to apply twice and sometimes 3 times to get the old paint off. I've been wanting to try Citrus Strip because it's less harmful to the environment and many people have raved about it.

That's about all I know about it.

I used citrus strip last weekend on my kitchen exhaust fan. It took 2 coats, the first for the latex house paint layer and the second for the original 50s enamel. Worked well when wrapped overnight with plastic wrap and I'm planning on using the rest to strip some painted clear redwood siding. Still can't imagine ever stripping a whole trailer.

Before:


After (bronze paint)

Today I tried the belt sander, vibrator sander, side winder 3400 RPM wire brush, and pure chlorine bleach.   Both sanders do nothing.  Bleach made the old paint look like brand new paint.  The 3400 RPM wire brush takes the paint off but it will probably take 3 weeks to do the whole trailer.  So new paint over the old paint when the weather gets warmer maybe next week weather man claims it will be in the 70s next week. 
 

Sand the old paint smooth and clean with a proper prep cleaner, then prime. You have to pay attention to what you have. Nothing will stick to powdery old paint.