As to what plants you have will depend on your set up. How your going to light the tank with 2-3 watts per gallon. (minimum for plants to grow well.) How much time your willing to put into a planted tank. What kinds of fish you will have? Water peramiters, type of substrait, if your going to use CO2 or not, if your going to supplement the tank with trace elements for the plants. There's a lot of thinking that you need to do before you decide weather or not to plant a tank that big.
My suggestion would be this. Use the 25g tank as your "trial" tank to find out if planted tanks are even your thing. Set up would be cheeper than for the 90. I would use either FLorite or Laterite/ gravel mix as the substrait. I've used both and have great results. Compact florescent lights would be a good thing to have. Those can get spendy. I think they are well worth the money.
If you want or need more help just holler. I'll be happy to help ya.
Rose
