From a hashrate perspective, both setups give you the same 4.8Th/s so in theory, your solo mining chances stay the same.
If you like tinkering,flexibility, and modular setups go for the bitaxe quad.
If you want simplicity and plugandplay grab the nerdQaxe++.
Either way,solo mining is still mostly about luck and uptime.

Personally, I’d pick 4 bitaxe units - just for the redundancy and fun of messing with the firmware.