Is one better than the other(especially for a novice)? I know it depends on the router, but what are the advantages/disadvantages of using these over stock firmware?
DD-WRT for me. DD-WRT has been in development longer and has a larger support group, IMO. Admittedly, I’ve not played with Tomato.
Stock firmware limits what your router can do to what the vendor wants it to do. DD-WRT maximizes the resources to allow for QoS (Quality of Service), virtual WAPs, logging, and tighter security. Many of them support CIFS sharing if your router has a USB port.
The chance of bricking your router is non-existent if you follow the instructions to the letter. I’ve installed DD-WRT on no fewer than 50 routers in the last 2 years with absolutely no failures. If it’s supported, it’ll work.
I am not qualified to answer that although I did read a little about Tomato before installing DD-WRT. I needed custom firmware to run an adblocking script (of all things) for Goggle-TV browsing (Logitech Revue) which doesn’t support ad-ons in Chrome.