I'm going to share my thought process of how to I'm going to choose my buddy in case if it's helpful at all to anyone else
I have 74 Mareep candies so this event could help me get my pokedex Ampharos but I don't have a good IV Mareep to evolve.
But I also have my only Tyranitar 97% IV just over 2000 CP with 5 candies with Iron Tail/Fire Blast so this event could help me either max it out (I'm a level 34 player) or get a second one with better movesets - but I doubt I'd get another good IV larvitar to evolve..
And then my other option is Blissey - I've only caught about 6 Chansey EVER, including the Valentines Day event, and walked my only good IV one to evolve into Blissey for a astonishing CP of just over 1200 with only 1 candy.. so this event could help me max it out
I did some calculations for how much I'd need to walk to get just the prefect amount of candies per option (TotalKm).
I basically did the amount of candies I need to reach my goal (C) multiplied by the regular km count to obtain 1 candy from your chosen buddy (BuddyRegKm), and in my case all my chosen options are 5 km, divided by 4 (4x as quick to obtain candy when walking your buddy).
Km needed to Obtain Candy Goal during Rock Event Formula:
(C) x (BuddyRegKm) / 4 = (TotalKm)
You can get the amount of candies you need to get to your goal through many different sites and apps that help you calculate power ups and evolutions, etc. but I won't go into that. But I promise they're not hard to find
For the purpose of the candy/km calculations, I won't be including the factor of increased larvitar family spawns to catch/get candy because I don't know for certain whether or not I'd even find any so it's not measurable for this.
Also, when I say "PER DAY" I divided the km # from the formula by 7 assuming I would get 7 full calendar days of the event
Here is what I came up with for my choices:
• to get my Pokedex Ampharos: walk just under 49 km which would mean I could probably complete in 4-5 days
• to max out my Tyranitar: walk 25 km PER DAY
• to evolve another Tyranitar: walk just under 22 km PER DAY
• to max out my Blissey: walk just under 30 km PER DAY
Of course this is if I can obtain my goal within the timeframe of the event which for me, isn't likely for the last 3 options. However, it gets me closer to my goal after the event is over.
You can see how close you can get to your goal by modifying the formula with your estimated km walk distance per day to get an estimated candy count.
With the help of algebra (stay in school kids ) , you can do the km you hope to walk within the event (TotalKm) divided by (BuddyRegKm) multiplied by 4 (quickness multiplier to get how much candy to expect from your buddy during the event (C)
Expected Candy from your Buddy during Rock Event Formula:
(C) = (TotalKm) / (BuddyRegKm) x 4
For example, if you choose a buddy that regularly gets 1 candy per 5 km and you know you walk an average of 10 km per day, you can assume you'd walk 70 (7 days x 10 km per day) km within the event. This would be your (TotalKm)
So 70 (TotalKm) / 5 (BuddyRegKm) x 4 = 56 candies to expect from your buddy
For me, the 10 km per day is more realistic so I can expect at least 56 candies from this event from either Tyranitar, Mareep, or Blissey which means I can definitely get my Pokedex Ampharos!
But because of how ridiculously uncommon Chansey and Blissey are for me and where I live (which is another factor to put into play that I again, won't go into. This is long enough ), I want to be that 56 candies closer to maxing out my Blissey
Plus, I'm hoping I'll see more of the larvitar family in the wild during the event for those candies
And I'm in no rush to complete my pokedex with Ampharos being one of my last,
but that's just me
Wow, this was such a long post
I hope it's helpful to at least one person!!