If you have the chance to try out either car, I would recommend it
(and preferably from drivers who know how to set up a car, so you get a good impression of what the car can do).
Also, what terrain do you drive on? I found the DEX210 is good out of the box if there is a lot of grip. However, when there is little grip (dirt, dusty clay) there are some design features on the rear end that make it struggle (not enough rear droop and high roll center). The droop issue is easily solved with a Dremel, the roll center needs additional parts or machining. (Note: I only drive the car in MM - that's why the grip issues on the rear exaggerate. Still, they may apply on the RM too). Lastly, I found the quality of some plastic parts is debatable: Not as accurate as that of competitors, and the plastic is so soft that threads strip relatively easily.
Problem areas aside, the car like I said is very good out of the box when there is grip, it's a very clever design which makes it convenient and fun to work on, and apart from the low roll center on the rear, everything is there out of the box to set up your car just the way you like, which makes the car really flexible between low bite and high bite tracks without buying upgrades
The BMax I haven't driven, so I can't comment on that.