I have the Big Baby Beast, the Cloud Beast and a couple Griffins.
The Cloud Beast (hate that name!) does leak/seep a tiny bit with an octo-coil installed. Not much, but enough to prevent me from wanting to carry it around all day in a suit jacket. I haven't built the RBA yet as my V8 coil is still going strong after 3 weeks of heavy use.
The BBB never leaks unless you overfill IME.
Both are amazing tanks. I would bring the BBB for out and about though. Smaller, never leaks and basically the same as the full size Beast.
A friend has the smaller Baby Beast and likes it but prefers his BBB. Same coils, smaller footprint.
My Griffins are great, but do leak a bit.
In any case, if I had to pick one, the BBB would be it. I own 50+ tanks and these TFV8 tanks are the best I have ever used by far.