I use and would suggest going with an 88 key , hammer action midi controller. A keyboard that has less then 88 keys will only be able to play a certain % of another sound modules notes, and you will have to laboriously stop what you are doing and press a button to midi transpose up and down to get to those other octaves. An 88 key keyboard with hammer action gives you a more realistic axe to play piano. Hammer action attempts to simmulate the mechanical feel of the piano's hammers striking the strings in a piano so I believe this is also useful when playing other patches via midi such a strings because it allows you to recreate with more accuracy the precice velocity.
Also why purchase a keyboard with sounds when sooner or later you will most likely only favor a certain amount of those sounds on the keyboard.
I suggest getting an older midi controller like the kx88 , or roland a80/a90 which are favored for their realistic hammer action even compared to todays modern 88 key hammer action midi controller because of their superior build and production cost from back then.(kx88 and roland a80/a90 have the same mechanical device for their feel but the kx88 is supposedly tuned to have a heavier touch.) You will most likely have to pay to get the felt replaced on those two keyboard.
If you want to buy something new then the maudio keystation 88 pro is probably your best purchase.
http://www.zzounds.com/item--MDOKEYSTAT88 This thing is great in reason 3.0 because you can assign all those knobs and sliders easily which give you total control of the many parameters of a sound module.
