That is a wide question:
Are you going to be doing web, corporate, broadcast or all of those productions?
What camera feeds are you using? (Composite, S-Video, SDI, HD-SDI)
More importantly, how many cameras will you be using?
Will you be doing virtual studio and/or stereoscopic production?
How portable do you want it to be? (flight-case, van or truck)
Then you need to consider audio, sync and talk-back.
We have both a tricaster and a blackmagic atem switcher here at our university. Our students have used them both for creating they're newscasts. My opinion I prefer the tricaster. I can't quite nait it down but for me the atem is a bit more finicky. The set up and configuing of the Tricaster is a quick and easy. Are you planing on getting a control surface for either? We installed the touchscreen version of the atem and i'll tell you its not as responsive as I would want it to be, plus there is just somthing to pressing a physical button.