Man, a loaded question for sure. Several more questions for you:
Are you looking for more scale appearance?
What size, 24th (SCX24) or 18th (TRX4M)?
Trail or full tilt boogie rock crawler?
Both have unlimeted uogradeability as already mentioned. However, those two options are like comparing oranges and grapefruit. Yes, they are both citrus, both delicious, but eaten at different times of the day.
You can also put several hundred dollars into each one in upgrades...which can be a lot of fun.
Also as mentioned, for 18th scale, the Redcat offerings are amazing, and really not many rigs are comparing to their capabilities right out of the box. Especially the Acsent 18 Apex. The Apex is a little more up front, but holy smokes what a rig! No upgrades needed at all.
But back to your original question, if it were me, between the SCX24 or TRX4M, I would go for the SCX24.