I'm firmly in the bigger is better camp. The only real exception being where time is not a premium. When I was a lot younger I had plenty of time to mess with small tanks frequently, and could do daily changes if I wanted to. Now I run understocked bigger tanks so that I can have some leeway in my maintenance as time is a premium. There are ways of making maintenance easy if you have long enough arms. Overall the limitation on a tank is space and price. Larger tanks do come with a bigger electricity bill as well though, but there are ways to keep that down.
So my answer is, how big is the gap and can you fill it with tank? If so, go for that.