I've seen Candii and she's gorgeous, sexy, and an excellent GFE (in my opinion). Worth every penny and would love to see her again. Lexi has been on my hot list for a while now and and I've tried booking her once but missed out. I see her as pure PSE judging by her profile and I would love to experience what she has to offer.
I think Candii is more expensive than Lexi but I can't comment on that since I haven't seen Lexi. In my experience the cheaper ones are that for a reason but I'm happy to be proved wrong.
For me, as far as I can tell, they are nothing like each other and cannot really be compared.