Got WRT1900AC.. works like charm...
I get really good connection... approx. 3 times better than EA3500... 2.4 & 5Ghz.
i've updated FW and it's rock solid so far.
I went the opposite direction actually - after buying both the WRT1900AC and AC68U - I decided to keep the AC68U and run the RMerlin firmware on it.
I thought about it in the following manner:
1. Reliability: This is probably the biggest gamble I'm taking despite being the most important issue. The WRT1900AC worked fine for 3 days without any issue. Been running the AC-68U with the rmerlin firmware and it seems to run fine overall. I get strong 802.11ac connections on a macbook air and htc one on both devices but a weaker 802.11n connection on the Nexus 10 despite being one room over from the router (sitting in a closet) - could be a Nexus 10 issue. I still feel the WRT1900AC might be more stable but might just be a perception issue on my part.
2. Router Performance: Most of the benchmarks on the web show that the AC68U is at least comparable if not better than the WRT1900AC on the compatibility front. Anecdotally, using my webpass connection - I get anywhere from 200mbps to 550mbps download and upload speeds from both routers to my PC so they seem pretty comparable. I'm in the process of moving so haven't added in multiple devices and etc... yet.
3. Features: Focusing on what's important to me, AC68U has time machine support while the WRT1900AC has much faster usb transfer speeds. It seems like if I really needed high performance storage, I would just buy a dedicated NAS rather than rely on the USB3.0 port on my router. Time Machine as a convenient backup solution is much more important to me, especially since most of my life is stored in the cloud anyways between amazon prime, spotify, dropbox, onedrive, xfinity and etc.
4. Chipset: I'm skeptical the Marvell chipset will be embraced by the community even if Linksys is fully cooperative in releasing code. The market share for the broadcom chipset is significantly higher and likely will continue to receive greater attention from the community unless something happens. Based on past precedent, I'm also really skeptical that Linksys will add any new meaningful features so any additions will have to come from the community which makes this an issue.
5. Value: Given the above, I think it's hard to justify the $50 or more price premium on the WRT1900AC over the AC68U. The only way it would change is if the AC68U is still unstable which doesn't seem to be the case with the RMerlin firmware or even the latest stock.