In all truth, I have personally never seen any difference between targa and .jpgs in terms of render time, resolution (appearence) or file size.

I use targas because, when I import them into After Effects, there's a little checkbox that quite simply says "Targa Sequence"...check that, and it imports my whole image range.

As I said before, I've never touched Premier, but I can't imagine a high-end compositing/movie-making program NOT having something so basic and useful like an import-image-range feature.

If you want, though, you can wait for other SM forum borwsers to come along and give you some more advice in image choices (.jpg versus .tga), if there is any.