I had an integrated Sirius for a while. The Kenwood head unit I bought came w/ a hardwired, integrated Sirius kit for free. I did not like it much. The head unit only has one line for display, while my plug-and-play set has 6. Now you can see the artist, song, channel, time, etc etc w/o pushing buttons. That's handier than you might think. It's also nice to be able to unplug your set and bring it inside w/ you ... or into another car.
One piece of advice: go for a set w/ a commonly available dock. My Audiovox set is great, but it is impossible to find docks for it anymore as it is discontinued. The newer Sirius sets have these universal docks, which means the dock is shared across several models. This should make finding docks easier.
2003 Ford Ranger FX4 Level II - Silver - Stick - fuelly
2009 VW Jetta SportWagon SEL - Grey - Stick - fuelly
2001 Suzuki Bandit 1200 - Red
Mildly Obsessed With Photography