Well, Nvidia mainly make (but not just) AMD based motherboards and Intel is obviously for Intel, so you are covering pretty much the whole market.
When it comes to Motherboards, I would simply get the cheapest from a good brand that supports the CPU and Memory you want.
For me, this usually comes down to a Gigabyte, Foxconn or Intel own brand with 4 memory slots, 4 Sata slots and a variety of other things. (To me, the most important at the moment is uses just solid state capacitors).
Again, it is really hard to give general advise - there are hundreds (if not thousands) of boards to choose from. But I hope this points you in the generally correct direction.