If you think you can get another very soon, and you REALLY aren’t sure, then it doesn’t hurt to wait a bit. If not, then it’ll still make a great addition to your team. Really, any Mewtwo is a good one, but I get your indecision.
Personally, I’ve been sitting on an 80% with 15 attack that I’ve been considering recently… and I have plenty spare rare candy… and stardust…