Everyone will have their own opinion here but you need to do some research. You will want to get at least a 4 quad with 2 gigs of ram. Storage at least 5 gig if expandable that is a plus. But here are some things to think about.
To give you the best viewing options, get a box you can put Kodi on it. That way you can stream plenty of movies and TV shows from other sources as will as give you multiple options for Live TV.
Some box manufactures such as Avon do not allow you to side load apps so your stuck with what they allow you to put on the box. For example if new updates comes out for Kodi or any other app your running, you cannot install it on your box until the manufacture updates their app store. Personally I refuse to get a box that does this, it is my box and I want to be able to put what I want on it. Yes you can probably root the device to allow for this but that normally voids your support and warranty especially if you brick the device.
If you want a box that you can easily get, then get a Fire TV which you can get at most large electronics stores such as Best Buy. These are good boxes and allows you to side load apps, however there is a learning curve on side loading the apps but plenty of instructions can be found on how to do this. Fire Stick will work but is a lot slower and only has 1 gig of ram so you need to watch on what you put on it.
If you only want IPTV and plug and play, then the MAG would be the way to go.
If you have a 4K TV then you will probably want a box that supports 4K.