IMHO any modern FBL controller needs to have self level/rescue functionality to be considered 'top drawer'. The Microbeast does have that capability but you need to pay for the 'Pro Rescue' upgrade (about $100 ?) on top of the basic price. The BD 3X doesn't have this feature, so personally I'd rule it out unless it was very cheap. The BD 3SX does have self level and rescue but I'm assuming the Axon is replacing it, so personally I'd go for the Axon unless the 3SX is very heavily discounted.
As for the choice between the Microbeast and the 3SX/Axon... A lot depends on price and your preference for setup method. The Microbeast uses programming via the Tx involving wiggling sticks and interpreting blinking coloured lights. I MUCH prefer the more intuitive PC software interface that almost all other FBL use, but I know some like the blinky light thing, each to their own.
Personally I'd not go for either of them, I'd go for the Spirit Pro, it's cheaper and it has more features. The Spirit has integration and telemetry support with a wide range of transmitters and a GPS module interface is coming shortly, and it has the best stabilisation and rescue options in the business, plus it's easy to setup and flies great! The only minor gripe I have with the Spirit pro is the top entry connectors, but that's the same as the BD units anyway. IMHO the MSH Brain2 is about the only FBL that runs the spirit close at a similar price point.