Dont walk a machop, its not worth it, as a buddy it is perhaps one of the least worth it to walk because candy can be gotten elsewhere much easier, you can get the candy from machamp raids, egg hatches (they seem very common for me) and also research encounters, somewhat similar story for ralts and larvitar in raids
Togepi's a great choice, im walking one myself , its a 3k distance so it gets candy faster, and i dont think it will get an event due to special evolution requirements, Beldum and bagon are also good options as both are likely to get community days sometime soon if they are going to do all the pseudo legendaries (than and you'll want to walk them before garchomp gets here)
Chansey or blissey can be slotted into gyms and grind for candy by feeding berries (works better than expected with how long they last, GRB'ing mine and a friends yesterday and got 2) Dratini can be similar as dragonite's a good defender, but on offense it is good and with the prospect of possibly rayquaza and the gen iv dragons soon, you'll want all the dragons you can get. (note that gardevoir and togekiss wouldn't be effective agaisnt dialga due to steel type, and gardevoir would be a no-go against giratina because ghost type)
I think you're best bet's a bagon or beldum, then dratini or togepi buddy as you have a lot of candy for dratini and togepi gets them faster, if cant do tyranitar raids, then larvitar takes priority over togepi
