I'm a beginner and i have had a 2.5 gallon tank with a betta and 4 danios in it for almost 6 months. I want to move to a 20 gallon (or possibly a 29). I'm not sure if u want saltwater or freshwater. And what would be some suggested fish for each?
Being as you are new to the hobby I would suggest that you try to plant your future 29 gal and give that a try. From what I understand the larger the tank the more successful you will be with a saltwater tank - I think 29 is far too small for a first try saltwater.
For a freshwater tank there are lots of neat little schooling fish to try. Surf the web for lots of ideas...
Pretty much everyone will say that, as a beginner, you shouldn't try a saltwater tank of less than 50 gallons. Apparently, saltwater fish are much more sensitive to changes in water conditions, and the larger the volume of water you have, the smaller the effect of small chemistry fluctuations are (if you think about it, the ocean is a pretty big tank ).
Plus, saltwater tanks (unless they are fish only) are much more expensive to set up. Reef tanks can easily cost $50/gallon.
Personally, I'd suggest a tropical community tank. Fish selection is really a personal choice, but I'd suggest getting a couple of top-dwellers, a half-dozen or so small schoolers, and a few scavengers on the bottom.