The economics of tank maintanance is one thing to consider, as the costs (supplements, water changes, etc.) go up as a tank gets bigger.
Another issue to consider is the height of the tank. Make sure that the tank isn't too large that it limits your access. For example, I used to have a 150 that was 29" tall. That tank was a pain to work on because I couldn't reach the bottom if I needed to, and I'm fairly tall. I currently have a 24" tall tank, and will be setting up a 25" tall tank this summer. For me, that's about the maximum height that I'm comfortable working on.