SEI, Sadlak, Bassett all work well. You can find hem used on M14Forum all the time. I like the Bassett mount because it uses 1 screw to mount and is super easy to install. The Bassett mount uses the groove in the receiver to match up and help to hold zero. If you get the high Bassett with can still use the iron sights. But if using the Bassett make sure the groove is clean and still sharp. If not then look at the SEI. The SEI mounts into the stripper clip guide and can be a pain to install but once its in, as others have stated, its rock solid.
Cant go wrong with any of them, just how much do you want to spend and do you ever want to take it off.