Love bugs are out in May! If they bother you, go for August...
We've been both times and while nothing will keep me from accepting a trip to Disney at any time, love bug time is my all-time least favorite...August heat 'n humidity truly is horrific...but if you expect it, travel early or late and move around between a/c buildings and buses (or hang out in pools) it's tolerable...May weather is glorious, but those cursed love bugs do "bug" me, a lot! As noted, it wouldn't keep me from going if a chance to go in May came up...but if. like you, I'm choosing between two alternative times, I'd go for August and heat over May and love bugs! On the other hand, May arrives sooner than August and I'd always rather be at Disney...so maybe that's a reason to choose May!