Art,
I'd suggest using a quad band model as that will provide you with the best coverage. Even though most of the cell networks in Germany operate with both frequencies, the 900 MHz frequency provides better coverage in some circumstances (inside buildings).
One point to note: AFAIK the 2100 MHz band is only used for data, so that's not something you'll need to have for normal voice or text.
I travelled with a tri-band phone on a trip in 2004, and it worked reasonably well in the U.K. However, I've had a quad band phone since then, and never had a problem with "crappy coverage". Most places in Europe have great coverage!
So far I've used roaming with Rogers, and the costs have been reasonable (using text most of the time with very occasional voice calls). However I may try one of the "travel SIM's" on a future trip just to compare costs. Have a look at Cellular Abroad, Roam Simple, Call In Europe, Mobal or Telestial for examples. I'm not a big fan of using multiple SIM's while travelling.
Happy travels!