I came from a Geo with GST kit and now I have an NT so I can give you a decent awnser, not some fanboy stuff like some posts here.
1: They are both spoolvalve markers. The GEO with the GST kit is super smooth and quiet without any kick. The NT shares the same thing, maybe a bit louder but nothing I personally bother. I notice my NT is shooting way more ball on ball accurate then the GEO. I couldn't believe it when I played with the NT at first. Real sick!
2: The bolt of the NT is not all the same but has some parts that look like GEO parts. The NT bolt has more O-rings and is a little bit more difficult to get apart. Personally I don't bother because I maintain my guns always after every day of play and I'll take my time on them.
3: The efficiency of the GEO is like every other spoolvalve marker, not that great. The NT has WAY better efficiency. Without tuning the bolt the NT can shoot 10 pods easily on a 4500k fill. I always fill my tank after every Xball round so personally I don't care about the efficiency, as long as the marker can shoot 6 pods and a hopper at least without getting problems.
4: The NT is one of the lighest markers out. So if your looking for that, the NT wins on that point. How it holds is personal. The NT is my big favorite here, this gun is so ergonomic, butter!
5: I like the trigger on the NT way more then the Geo. But this is offcourse again personal.
6: The missing LCD screen, I don't care. I set my NT to 10.5 Millennium mode with the good allround dwell setting and it's done, I never have to switch modes. I got the Virtue board, so IF I need to change, it can be done without removing the grips.
7: About the grips, the NT is a big favorite here. When you get the feeling for it you can switch the battery under 10 seconds. I really like the tool-less design!
8: ASA, don't know what people are talking about. It doesn't feel cheap. The big difference is that the macroline is comming out of the front. For me this is a big pro. I want to play as tight as possible. On the geo the macroline fitting is sticking out and blocking my wrist. On the NT nothing is, really like it!
9: Price, the Geo is like 500/600+ dollars cheaper, so if price is important, the Geo wins offcourse. I don't care, I earn enough money so I don't feel a couple of, in my case, euro's more.
10: The NT is a brand new design and has some new technology. Every first marker from a brand new serie has it's child deceases as we call it here. The Geo had this as well. Make sure you got all the updates if you are going for a NT. The GEO will always have the updates it needs because it's way longer released.
Hope it helps a bit. Don't listen to fanboy's. Maybe you can shoot them both somewhere and make your choice! Goodluck!