I use INK London but I have also been on a See & Try Day with Ikon.iq and was impressed with them as well.
I have stayed with INK because I’m very happy with them and don’t feel the need to introduce another brand but if I was, I would certainly go for IKON.IQ. I appreciate this isn’t really much help, but I think both brands are good quality and trustworthy, so in my opinion either would be a good choice. Why not get trial kits in both and see which you prefer?
Ikon has a different application technique, and I see some techs struggle with it to start with, so I think a conversion course would be worthwhile and I understand it’s reasonably priced.