Is it a WDR3600?
I would decide first whether you really want to try dd-wrt.
It appears there is no easy way of going back to stock firmware if you don't like it (I did manage to get back to TP-Link firmware but for some reason the WAN wasn't working, so I'm now stuck back on dd-wrt, other branded routers are apparently much easier to revert). Just managed to get mine back to the TP-Link firmware. It was apparently an issue with the Superhub 2 and MAC addresses. Just took a few resets and restarts on both the router and superhub 2 to get it working again.
I updated the stock firmware to the latest stock firmware from TP-Link (apparently it adds a recovery mode that can be used via tftp), then upgraded the firmware using the 'factory-to-ddwrt.bin' from here:
ftp://ftp.dd-wrt.com/betas/2014/11-11-2014-r25309/tplink_tl-wdr3600v1/
You then use the 'tl-wdr3600-webflash.bin' files whenever you're updating to the newest release from a previous dd-wrt release. r25309 seems quite stable so far, haven't found anything that doesn't work. r23919 is apparently another good one. Don't use r24461.