forget, abs unless you intend to enclose the printer.

For flexible filaments - The easiest one to use is polyflex from polymaker.

Your best bet is to go here: http://www.globalfsdusa.com/?target=main
and buy some samples to test out. Saves on money by not buying a big roll you might not like.
We all seem to have different experiences with different brands so it's best to try as many out for yourself as you can.