I use Bter a lot - I like their style and they're very reliable. Use cryptsy a bit - don't like how they manipulate markets in advance. Use quite a few of the others. No reason why apart feom the fat that spreading makes selling high volumes easier
FUD always happens. If you're threads are constantly being bombarded by people spreading FUD, you can make a self moderates thread. However, people may question your reason for doing so and may accuse you of all other sorts of things by fring to cover up stuff etc. To be honest, the best way if dealing with FUD is by ignoring it. Keep posting good stuff and let people do the math for themselves. If people here only believe what they read, then this isn't the right place for them. They need to invest in wha they believe is good and what suits them after doing their own research.