None of them. I already have 22 raid passes clogging up my bag that I can never use anyway, so I really don't need more of them. I've only been able to get a group for 1 Groudon raid in the last two weeks, so I've only even been able to use about half of my free passes lately, on junk like Marowak and Scyther raids. Fought a Magikarp today just because I was still on yesterday's pass, so at this rate, I might need more premium passes some time in October or so.
I want either a discount on storage upgrades, or a real discount on incubators, not just super incubators for the same price I can buy regular ones any time.
Right now I'm not sure I'll get a box. I usually end up buying atleast one, but this time I don't really need it's content.
Incense - I rarely use it and have 24 in my bag, which will last me a very long time.
Pinap Berry - They might be useful to get extra candies, but I get enough of them from Pokestops, so I'm not interested in paying for them.
Star Piece - No. I got loads from buying the last boxes and have used very few (usually only when I've hatched several eggs at once). I currently have 56 and that will probably last me until 2019, atleast.
Max Revive - Can't remember the last time I struggled with lack of potions and revives, so buying Max revives isn't worth it for me.
Lucky Egg - As someone who is still 6 million XP from lvl 40, these are of course useful. But I have 32 of them and it's not like I use them all the time.
Raid Pass - Now here's probably the thing I would be most interested in getting, but I have 29 of them and usually only do one raid per day, sometimes not even than, which gets me an extra pass for the next day.
I would actually rather get some incubators, but maybe we'll see that during valentines day.
Anyway, if I were to buy a box it would be either the Great or Ultra box.
If I'm only after the raid passes, then the Great box would be the best seeing as it saves me 120 coins. The Ultra box only saves me 20, but if I suddenly want more Lucky eggs, then that box would be worth it.
The problem is that I'm already struggling with limited space in my bag. Even though my bag is maxed out, I still hit 1500 every day and have to get rid of things I might want. So the Ultra box really doesn't suit my bag.
Finally, we've had quite a few boxes recently and I suppose we'll see more in the future, so even if I skip buying one this time, there will probably be Raid passes and other stuff available again fairly soon. Hopefully will less Star pieces, because I'm really tired of them.