If you had to pick one island...?

Do you mean in addition to Vis (I just replied to your other post)? Vis has all of the above at that time of year.

Hvar and "not too touristy" probably sound odd together, but in May I found it pleasant, not too crowded at all, and you can always stay in a town other than Hvar Grad. For beauty, Hvar wins.
I've heard great things about Milna on Brac, but I have not been there.

Mljet also has beautiful scenery, and it isn't touristy in May. Not sure it's the best place for cafés though, I'm sure there are some, but people go there mostly to enjoy the island's natural beauty. Hvar would be the place to go if you want to sit at a pavement café and watch people go by.

I'd choose Hvar, for the very nice cafe scene and overall beauty. No place will be touristy in May (or even June, compared with most of Europe).

I second Hvar. Absolutely loved it there. Lively, beautiful, fun -- what more can you ask for. We ended up cutting out one of the islands to stay there longer!

Hvar 100%

take catamaran at 11.00 Split - Hvar

freey leave at 8.30 but 2.5h

Thanks everyone, looks like Hvar wins. As for my previous post about
Vis, I was trying to figure out which island to go to to get to Italy and now I've decided to make my
way back to Dubrovnik and leave from there, so now I have more choices of which island i can go to.
Thanks again

If you only have 2 days, Hvar, but if you have more time to spend on an island, I would still consider Vis.

Hvar. Take a boat trip whiel there.

Hvar for me also.
As others have said you can take day trip from there to Brac or VIS etc if you wish also. It will not be too busy in May. I was there in spetember and even by then the huge crowds had gone.