Is making a Larvitar/Dratini your buddy even worth it?

There are really only a few pokemon I would ever recommend using as your buddy, everything else is suboptimal considering you will catch / hatch them regularly. Here's my buddy ranking, but it's open to interpretation based on biome:

1. Snorlax
2. Chansey
3. Dratini
4. Larvitar

Snorlax and Chansey are probably the best choices in my opinion, but if you're in a desert biome for example, you may give less weight to Chansey candies. Dratini and Larvitar can be swapped around based on biome, but I give those less importance than Snorlax / Blissey because they can be "farmed' a lot easier.

I would pretty much never have a buddy that isn't one of the above pokemon.

At the moment and how the game goes the only pokemon really worth walking for are: Snorlax, Chansey, Dragonite and Tyranitar. Gyarados, Vaporeon and Rhydon should come with time without walking, Lapras got nerved and Golem and Exeggutor are not relvant in many areas anymore. Of course every player needs a Jolteon or a Fire-type, but that should be achievable without walking, too.

You ask a pretty complex question that only you can answer correctly. It depends on a lot of things like how many eggs you hatch I guess. For me I hatch a ton of eggs so I could walk something else and still probably get one of those two in not too terribly long. But then I have to power it up and what 3KM pokemon is more useful than those two if you get a good moveset?

Maybe the best question is whether anyone on the planet would trade 34 3KM candies for 20 5KM Dragonite or Tyrannitar candies? I cannot think of a scenario where I would. So my answer would be for me I would stick with those two or maybe Blissey.

It depends on your preferences but I personally would never walk a 3km or 1km mon, always stick to the 5k ones, the most rarer, like Dratini, Larvitar, Chansey, Snorlax or Mareep, the rest of them have nests, and a lot higher egg chance, 2k and 5k are probably like 100 times more common than 10k and on TSR you can find nests for all the rest of mon you need to complete your dex.

I have made the same mistake on the past, walk mon like Charmander, Machop or Geodude just to hatch them after or see my local park become a nest of them. Geodude was a big slap on my face, after walking a lot to get Golem I hatched 6, yes 6 in a row from 2k eggs, and I better don't talk about how much it cost to get Charizard and soon after a park near my home became a nest (also the new year's event).

If you take the advice, stick to the rare 5k mon that you will evolve/power up in the future, those you need 125 candies or are top tier defenders/attackers, the rest will come with time.

I say go for it. I've only encountered 6 dratinis ever, never hatched one, and I've been walking with a dratini quite a while now. Still not even halfway to 125...
Although, the unthinkable actually happened yesterday. Opened the app and there in the bottom of my screen, a black silhouette I was certain I'd never ever see on my sightings, a wild dragonite at a pokestop!
Rushed overthere in a hurry and the orange dragon suddenly popped up on my map! Tapped on it, 1260cp. Unfortunate, I thought, but hey it's a freaking Dnite! Fed him a berry and threw a great curved ultra ball at him. I was sure it'd be a first throw catch, "nite, nite!" I thought.
Well, short story short, dragonite was in no mood, said "night, night" and fled after my first throw.
So yeah you walk your dratini and I'll keep walking mine and hopefully, we've got ourself a dragon by the end of this year!

There's only a pokemon worth walking with as a buddy at the moment:
Chansey
(Blissey works too lol).
All others are suboptimal imo.

Still, if missing few candies for a crucial evolution, I would go for a 3-4 candies walk with a Larvitar.

Ultimately it comes down to how you play the game (and there is no wrong way to play, it's your game). Personally my policy on buddying is a mixture of what's been said above. I would only buddy for what I consider 'premium candy' - basically any Pokemon that isn't common, and doesn't nest, and whose candy is of value for either leveling or evolving. If you pay attention to nest migrations and are prepared to do even a little travelling to get to one, you WILL, over time, find a nest for any nesting pokemon, and when you do you'll suddenly regret ever buddying with one.

For me viable candydates (see what I did there?) include Snorlax, Chansey, Dratini, Larvitar, Mareep, Lapras (although this is obviously much less rewarding now...), Grimer (just for the first evolution for the dex), and likewise with Porygon (although the valentines event probably makes that unnecessary).

As I said though, everyone's game is different. Some people just want to complete the dex, and have no training/battling inclinations, in which case this really goes out the window and they should buddy with whatever they need. Personally, I occasionally break my rule by buddying with my Gary, cos none of the areas I generally play in are water spots with regular Karp spawns, and it's only 1k/candy. I think a case could also be made for Togepi, particular for anyone with an eye on gen 4 (Togekiss is my favourite...), but I have a feeling there'll be an event for it at some point (Easter, possibly...?).