I would go for a 29 gallon. This is a great size for 90% of the fish out there. It is also big enough that with regular water changes, it can be very stable. For a beginner, I would not go bigger. It simply gets to expensive, and to overwhealming to quickly. Plus, beginners often loose quite a bit of fish at first, and a 55 gallon can become difficult and expensive for a beginner to keep properly stocked.
Also, the aquarium bug doesn't bite everyone. if 2 months down the line you are bored of the hobby, at least you didnt put to much money into it.