Power up or Evolve?
I have recently caught an 80% lv 20 Rhydon with mud slap and stone edge, even with not so good IVs he still a very good pokemon to put in gyms if I power him up.
I also have a 96% Rhyhorn at lvl 16 that I would really like to evolve, but I only have 57 candys. My only good defender is Exeggutor and all gyms around are already full of them, as snorlax, lapras and dragonite are very hard to get I think rhydon is a good way out. Should I go only by IVs and evolve the 96% one ore spend my candies on the Rhydon?
Answers
Even if you evolve the Rhyhorn, you'll have no candies to power it up so at level 16 it will actually be useless in gyms. Plus you'd have like a 70% chance of getting a worse moveset.
And 80% IV isn't "not so good" by any means, it'd probably make something like a 50 CP difference when maxed out, and no difference at all in battle. So I'd say max out the Rhydon!
Depending on the stat distribution, if the stats were 8/15/15 (att/def/hp), then at lvl 30, it's CP would be 2722. For a 100% Rhydon, it would be at 2829 (+107 CP diff). In some areas, 100 CP would be the difference between middle tier and bottom tier of a high level gym.
I'd probably try to find another one and grind for more candies first, then evolve the higher IV one.
As more people hit higher levels, if you want to stay in gyms, I think you have no choice but to powerup/evolve high IV ones as your teammates are probably doing the same when they put a gym defender.