I can't help with the Buffalo, but I have been following the RT-N16 for quite awhile. There seem to be a significant number of people having trouble implementing the USB drive and printer functions. Large file downloads and frequent resets are a problem, too.
To be fair, other people report no problems. Asus is very slow to release new firmware to resolve these issues. I just bought an RT-N16 after becoming convinced that teddy_bear's version of Tomato for the N16 is stable and does what I need.
I tried the router with factory firmware for simple functions like email, surfing and downloading single files (no P2P, USB or Print sharing). It worked with no issues, but seemed sluggish and pretty much the same in all respects as the WTR54GL that it is replacing. Wireless range and speed on G was similar to the old Lynksys.
When I installed Tomato, things got a lot snappier. Pages load very fast. Wireless G is a little faster with more range and things just seem to work a lot better than the factory firmware. Zero connection drops in over a week. I have not tried USB, Print Sharing or P2P. I'm very pleased with the performance with Tomato. Not so much with the factory firmware.
I don't know why surfing is so much faster. May be because I used Tomatoes QOS to give DNS activity the highest priority.