If you want an alternative to Caterpie, go with Chansey. Chansey has a call rate of 9, which is pretty decent as far as call rates though
If you want to get more EVs than that, chaining Chansey in Poni Plains gives you 2 HP EVs per Chansey and 3 per Blissey.
If you don't want to try to find Chansey, which usually only takes 5-15 minutes for me, you can hunt for Grimer, which also has a call rate of 9. It can be found at Malie City Outer Cape with a 30% encounter rate.
Bonsly is good for Defense. It has a call rate of 15 (max).
Defense- I’d say Bonsly. If you break the rocks on Route 1, enter the grass and there is a 30% encounter rate for Bonsly. It grants, again, 1 Defense EV. It can also call Sudowoodo as its ally, which gives 2 Defense EVs when you beat it.
Zorua, in my opinion, is the best for training Special Attack. It has a call rate of 9 (pretty good).
Special Attack- This one is harder. I’d suggest Zorua though. At the Trainer’s School, Zorua has a 30% encounter rate. Beating a Zorua gives 1 Special Attack EV. It can only call itself when SOS chaining though.
Hope this helps! :)