So who's your buddy?

That's my question too. Currently walking Dratini since I know Dragonite just straight up has a bigger CP cap than Snorlax...I thought it'd be a better overall investment.

working on my first blissey evolution so it wont change for a few days

I switched from Snorlax to Lavitar today, but in part because I hatched two lavitars today (one with 96IV) that finally gave me enough candy to evolve a Tyranitar. I got Iron Tail / Crunch. Doesn't feel as bad now that at least in theory I can different moves. Mostly I'm glad I didn't get fireblast. Now I'm wondering if I should power this thing as much as possible hoping to get bite on it at some point. Have about 25 candies left so I"m just walking for now. If I hadn't hatched those I probably would have switched back to Chansey today since I had walked my Snorlax for a while. My Blissey is maxed but I only have 5 candies, and 1.1 million xp till the next level.

Walking Blissey. I still want one maxed out.

Blissey is for sure going to stay a stellar defender. But some others who will come into the Spotlight. Are Slowbro, Lapras, and Cloyster. Now that is just my speculations. I know for a fact that Ice Defenders will be very valuable because with only 6 pokemon alowed in gyms most people will just bring 1 Dragonite and 1 Blissey. So any pokemon who has a good amount of health and access to IB or AV will be very usefull aswell as Snorlax, Vaporeon, Donphan, Espeon, and Alakazam. Most likely.

A Larvitar, so I can max out my only Tyranitar. Or should I aim for a second one? Or would it be better to power up my only Blissey, which would mean switching my buddy?

More questions than answers - I'm really confused now :(

Tyranitar atm...although I may switch back to Dratini again soon.
I have Chansey candy sorted, and doing OK for Snorlax atm - although that will probably change soon as I feed my Lick/BS, as I wait for a Quick Move TM

To me, the only answer is Chansey.

Dratini isn't easy candy, but for most it is easier than Larvitar or Chansey.

And T-Tar is just too flawed for me....he is not a good defender, and his movesets are not great.

No indication that Blissey will be nerfed. So you either need to try to add another Blissey, or power up your existing Blisseys.