I"m no expert...but my .02 cents.
I think their are several models you will be happy with.
Milwaukee 2697-22 M18 18-Volt 1/2-Inch 2-Tool Combo Kit (5 year warranty battery meter on batteries)
Hitachi KC18DDL 18-Volt Li-Ion Impact Driver and Drill Combo Kit
Makita LXT211 18-Volt LXT Lithium-Ion Cordless 2-Piece Combo Kit
DEWALT DCK290L2 20-Volt MAX Li-Ion 3.0 Ah Hammer Drill and Impact Driver Combo Kit
I really think Lithum is the way to go!! I'm not a tool expert, but in other things Lithum has been used for a while (high end flashlights, computers etc). Lithum lasts a lot longer and dont' have the memory effects.
Pretty much their all 18V under load. Dewalt says 20V (good job markerting team!! lol), but its still 18V.
Their all around 300 dollars.
The dewalt has more BPM than the others....but the M18 has more RPM in the 1/4 impact driver by a bit. (the new dewalt brushless should be good, but its not in a kit that I can find yet and its almost double compared to the standard).
I would go to the store and check out the tools in your own hands. Since your going to be using it and not us. I really dont' think you can go "Wrong" with other of these to be honest. I"m not a brand snob.
I just purchased the Dewalt and it seems to be fine for what I"m needing it for. Just a guy needing to do some stuff around here, i'm not a contractor.
Whatever you go with I would make sure its Lithum!!
Good luck