Take Glaceon and Kyurem-C.
Competitively and in-game, Kyurem-C is obviously much better. It's the main reason Glaceon is not usable in OU: it's simply outclassed. Kyurem can run a very effective SubRoost set, is still good with an offensive set(particularly the Choice Specs set, don't bother with the Scarf one because it's outclassed) and it can screw over rain teams that don't have Keldeo.
HOWEVER, I will show you something completely ridiculous.
| 101 | Kyurem | 0.84462% | 16160 | 0.753% | 12088 | 0.699% |
| 155 | Glaceon | 0.30601% | 15982 | 0.745% | 11634 | 0.673% |
Look at the raw usage. You will see that Kyurem-C has only 0.008%(!!!) more raw usage than Glaceon. This goes to show how much love the Eeveelutions get. People tend to go "AWW LOOK AT GLACE IT'S SO KAWAII, SCREW THAT PIECE OF CRAP THEY CALL KYUREM" and then use Glaceon. I know Kyurem is ugly, but let's accept it, looks don't matter in-game nor competitively. Thank God the weighting system exists, however. Glaceon is only used by inexperienced players. If you are decent, you should know Kyurem is the way to go.