Celtics are a good 3 point shooting team, Bucks advantage are on the insider as its where there defense is focus, however, if these two will meat in the ECF, I would go with the Boston as they are not a one man team, everyone is willing to give their best and the are so unpredictable, and maybe they can beat the Bucks but their very good 3 point shooting.
Honestly, these two teams are my top picks in in the East so it's very hard to decide whether which one of them will make it. Hmm, I think I'll go with the Bucks. Their inside defense are stronger like what you've said and their 3 point shooting is not bad either (IMO) since Korver, Hill and Middleton were there; and take note, Giannis can now also shoot one 
. So for me they can dominate the East this year.