I prefer slip joints; they allow easy disassembly for future muffler changes, etc.

I always paint my exhaust parts with high-temp BBQ grill paint (from Wal-Mart) <img src="/forums/images/graemlins/wink.gif" alt="" />. This prevents rusting, and is much cheaper than the automotive paint, and just as durable.

It's also a good idea to install jamb nuts on the clamps; this prevents them from loosening.