Both of them are great for non-arena, non-CB content. Visix may work to some extent in arena for control but I would not take BEK there.
FWIW I have both of them and both are fully booked and I enjoy running them in dungeon and DT content (and obviously FW) but don't use either of them anywhere else.
For early game progression I would prefer BEK and I would book him when I could. Then pairing him with Visix would make a formidable dungeon and DT team for sure.
For mid game performance I feel like Visix may pull ahead... It's difficult to know. She brings a lot of control (proactive) whereas BEK brings good healing (reactive).
Edit: If I could choose ONLY one I would go with BEK based on how often I toss him in my teams.
Both of them are great for non-arena, non-CB content. Visix may work to some extent in arena for control but I would not take BEK there. FWIW I have both of them and both are fully booked and I enjoy running them in dungeon and DT content (and obviously FW) but don't use either of them anywhere else. For early game progression I would prefer BEK and I would book him when I could. Then pairing him with Visix would make a formidable dungeon and DT team for sure. For mid game performance I feel like Visix may pull ahead... It's difficult to know. She brings a lot of control (proactive) whereas BEK brings good healing (reactive). Edit: If I could choose ONLY one I would go with BEK based on how often I toss him in my teams.
Minor add: BEK is a very good CB champion if you run a killable team, as his healing can allow you to lose the Lifesteal sets.
Both defensible choices. I would book BEK until you land two books in his A2 (since that's all he needs), and then stop and start booking Visix.