Jan GE 6cG7 what other tube recommendations

I have never used the EI so I can't give comparisons to those. But I have the GE, Sylvania, RCA clear tops and chrome tops. Actually all sound very good to me. I think the RCA chrome tops are my favorite.
I bought mine on ebay.

I did read somewhere about the Amperex being a re-branded GE or Sylvania but I am by no means an authority on the subject. As Atmashere said all the vintage 6CG7 tubes are good.
I just like the sound of this tube. It's basically a miniature 6SN7. If your going to keep your preamp it is worth getting some tubes to try.
Just a note. If you are able to change the heater voltage from 6.3 to 8 volts. You can use the 8cg7. They are the same tube with a different heater voltage and you can get them cheap.

I find the RCA black plate to be good all around. Well balanced and good extension on top and bottom. That said the difference between the two different RCA's, Sylvania's and GE's is not that great. They are all fine tubes.

I have not tried the Raytheon's. I believe the early one's from the 50's to 60's were made in the U.S. Later production moved to Japan. "still good tubes from what I read". I think you may like any of the tubes mentioned. You may still like the EI's better? Rolling tubes can make you a little crazy:)