Depends, does it still get used at lvl 10? How many do you have? Do you have a lot of other and or better meat shields to where you don’t really like using them at lvl 10?
If it was me, if i had 4 lvl 10, i would lvl 20 1 and keep 2 at lvl 10. If i had 6 i would lvl 20 2 and keep 2 at lvl 10, something like that.
On my game i just made 6 Monostegotops, those in combination with my other herb meat shields has me not going to the 2 lvl 10 apato’s i have as much. I just have much better dino’s to use and never exhaust my bench in tournaments so i’d rather use better if i have it.
I’m gonna keep the 2 i have at lvl 10 more so for PvE, but again if i had 4, or maybe even 3 i would probably level a set up to 20.
In the end you can’t go wrong with either choice.