If you want it to be evenly bulky on the physical and special ends, you aren't using Calm Mind, and you don't need any SpA EVs to hit a certain OHKO/2HKO/whatever, then X-Act's Defense Effort Values applet suggests 252 HP / 20 Def / 236 SpD with a +SpD nature. However, in the on-site analysis (which is, of course, for level 100 singles), they use 252 HP / 252 Def / 4 SpA with a Bold nature. If you want Slowbro to be a physical tank (which is what it's best at), then that's what I'd use.Ugh, I hate doing defensive EVs. What's a good spread for Slowbro?