Good question. I don't have a definite favourite, but to come out of the recent series I would pick from Aftershock, Push To Exit, Foxic, Apex, Magnetar, Behemoth and Nuts.
Icewave definitely. I also like Predator (I like Danby robots), Monsoon and Petunia. From the classic Battlebots I would say Biohazard and Vlad the Impaler.