C is definitely the most common. If its syntax scares you you could always try
AmosPro and hope for the
Mattathias BASIC compiler to be completed so you can convert most of your AmosPro source code into C.
(AmosPro has a really crappy code optimizer so you'll want to use Mattathias for all of your compiling when it's finished anyway even if you AREN'T using a next-generation Amiga platform.)
Note: In order to use C on the Amiga you'll need to get the header files from
here.
