I was typing a big post about Flower Gift, since I think its merits are understated in this topic, however after reading like, ten times, Pwnemon's posts I realized that the cons probably outweight the pros and it can lead us to just not being a reliable answer to Politoed or being an absolute monster of a special wall in Sun otherwise. I'm still kinda well inclined towards this ability, so if anyone can provide good arguments to address Pwnemon's points on this, I'll be more than willing to vote for it.
For the other abilities, Harvest and Clorophyll stand out in my opinion. Harvest gives us a great amount of flexibility, and can address somewhat the problem of taking Draco Meteors and boosted Hidden Power Fires (yeah, somewhat, since we STILL need very, very good special bulk to avoid being 1-2HKO'd on the switch...). That's why Clorophyll is my favourite one at the moment: being able to outspeed in Sun means we can just avoid the OHKO with stats and punish it somehow. This may seem a poor argument or whatever, but I'm concerned about what we'll need to do to be able to deal with Latis without the boost of Flower Gift.
tl:dr - Supporting Clorophyll for now, unless someone gives solid arguments for Flower Gift.
Not accepting rating requests anymore. Sorry!