Seems like E4200 (not v2) runs much better than RT-N66U, performance charts compared in this site results are better on E4200, 5GHz stream beats RT-N66U on many tests, 2.4GHz stream tests are very similar to RT-N66U...
http://www.smallnetbuilder.com/lanwan/router-charts/bar/85-5-ghz-dn-3s
And... As far as i know Linksys does not have such bugs mentioned in this forum...
For those who need NAT loopback, apparently disabling HW acceleration, via the configuration GUI, is required.
For others it already runs fine without any settings changes.
Wifi performance (check the location charts) of the RT-N66U is better than the E4200 overall, especially in locations furthest from the router where it matters most.
I owned the E4200 for 10 months.
I ran tests with both routers (E4200 v1 and RT-N66U)., separately, using LAN Speed Test for throughput testing and my wifi utility for signal strength testing. The RT-N66U performed better.
The results for the E4200 are in my Amped Wireless thread. See this Asus thread for my Asus tests.
I do not use DLNA, so I can't comment on that.
I do know that multiple users have hard drives attached to the RT-N66U with the latest firmware and are reporting success. They can hopefully comment as to whether DLNA also works or not.
Asus is reportedly releasing another firmware later this month. As you can see they are quick to release updates.
The E4200 v1 had a media server issue (huge thread in their forums about it) that took 100 days for the fix to be released. This issue was introduced in a new firmware that came out 5 months after the router hit the market... I can't wait 100 days for a major issue to be fixed (luckily the media server did not affect me at the time since I was not using the USB ports on my E4200 v1).
Depending on one's wifi needs (if ones doesn't have clients located far from the router and / or simply don't need the best throughput performance and strongest signal in far locations), the E4200 v1 may be sufficient and is a very nice deal at $99 shipped for a manufacturer refurbished unit.
It does have far slower USB performance than the V2 though (v1 wifi is better than the v2 in some situations though).
You could try both the Asus and the Linksys and judge for yourself. That is how I made my decision (Tim's wifi tests helped me confirm my results - I also had only tested 2.4 GHz since that is what I use most, so it was nice to see that it also did well on 5 GHz).
Buy whatever works best for your needs.