I have several commons on my team in arena 7. Allo is a key player, but my ultimate is deinocherus. I adore her. She’s fast, she’s fierce, and she can take out most raptors in one shot (first, if she’s got her speed increase going). And when she does die she’s usually gotten my opponent down low enough that I can take them out with the next dino. She was ubiquitous around here before the big update; less so now, but still pretty common. I’ve currently got her at level 18, and I’m still sitting on enough DNA to level her up twice because I catch every one I see. And the best part is, people totally underestimate her in the arena, especially higher up, because she’s a common. But the commons can do a fair amount of fighting at higher levels which it takes rares, epics and above MUCH longer to get to.
In summary: pick a common you like and focus on it. Utilize it. And have fun!