PSXFerrari, you've made your point and there's no need to repeat it.

Anyway, I would recommend the Nintendo version, with the Tengen version being something to pick up on a multicart. Aside from the inflated price and lackluster 2-player gameplay you get with the Tengen version, it also has a very gradual speed increase that makes it really drag on. By the time you have 100 lines in Nintendo Tetris, the pieces are falling at drop-speed, whereas you need to get several hundred lines in Tengen Tetris in order to reach the same speed.
Even if you want to play with a bunch of people, the Tengen game is lacking because turns take forever, and there's no way to restart a two-player match, making head-to-head sort of pointless.