Lionel is one of my all-time favorite names. If I ever got to name an actual human, it is very likely that that would be the name they would end up with. Also, it reminds me vastly more of model trains than of lions.
Leonel I haven't heard before, and I can't say I'm fond of it. It just strikes me as a not-as-cool version of
Lionel, rather than its own thing.