I have all three... Ego Prime, Ego CSLs (Ego 11) and Ego LV1s. So probably can offer an opinion on them.
As has been mentioned, all Egos prior to the LV1 are very different. I bought the CSLs as I always buy the SL variant from PE. I really loved the CSL, but when I got the LV1, they stayed in the kit bag. I bought the Prime because I was attracted to the design and also intrigued about the differences. I havent really used the Prime that much, but when I have it did shoot very well. Plus I believe aspects of the science behind the Prime has been incorporated into the LV1 (@
Robbo should be able to confirm)
So if I had to pick one... I'd probably go with the Prime. It looks amazing, there are very few around and I like the way it's shot. An LV1 is still a great choice, but the Prime just ticks more boxes right now