A tough question. I suppose it depends what you want to do with the router. I've had a WRT54GL running Tomato for the last 4 years. It has never given me a lick of problems, and Tomato is great.
The E1200 as yet doesn't support third-party firmware, and it's unclear if it will.
Questions to ask yourself:
-How big are these files you plan to transfer on the LAN? If they're not especially big then G would be fine.
-How important is third party firmware to you?