I would highly recommend the Apple TV 3. I've had a version 2 and recently got the 3 which has the added bonus of 1080p output which makes a big difference to the picture.

It's also very easy to use. I'd recommend using wired connection (Ethernet) especially if you have a 3 as you'll be streaming more detailed files.

I use Handbrake to import my movies onto my iMac and have them stored on an external hard drive.

Only negative I suppose is that the online movies through iTunes are not very cheap but you do get to watch them in a 48 hour period. Also you have to have a machine running with iTunes installed which I have no problem with but I know people may.

Overall a great product, easy to use and relatively cheap to purchase.