I highly recommend trying both a long arm and a sitdown machine to see which one you like best. When I was in the market for a quilting machine, I just assumed I would prefer a long arm. I had the space and the money for it, so I went to try one out for a while. Luckily I lived near the Nolting factory and they let me play on various machines for almost 2 hours one day (great people by the way - take a look at their machines too). I discovered, to my utter surprise, that I didn't like long arm quilting at all! Yes, it was faster, but I truly missed the feel of the fabric under my hands. I did not feel connected to my quilt when moving the head instead of the fabric.
Some people find standing at a long arm tiring. Some peple find moving the fabric on a sitdown tiring. Best find out for yourself which one works best for you.
Pam