R/S/E: Route 113. Spinda have a 70% encounter rate. If Emerald Slugma also gives SpA Evs raising it to 95% chance to get hp evs per battle.
FR/LG: Pokemon Tower. 90% Spawn chance on Gastly and Haunter.
D/P/Pt: Resort Area/Old Chateau. Either 100 % Psyduck spawns or 90% Golduck spawns in Pt while surfing in the Resort. 100% Gastly spawns in the Chateau
Hg/Ss: Ilex Forest. Surfing in Ilex Forest is guaranteed Psyduck/Golduck.
B/W/B2/W2: Celestial Tower. Litwick and Elgyem combine for 90% encounter rate.
X/Y: Frost Caverns. Vanillite and Smoochum Hordes add up to 65% encounter rate.
OR/AS: Route 119. 100% Oddish Horde Encounters.
S/M: Trainers School. SoS chain Magmemite for double the evs per defeated mon.
US/UM: Any of the Meadows, or Brooklet Hill. Oricorio gives 2 per KO in the meadows, but can be hard to SOS chain effectively at times. Psyduck at Brooklet Hill are slightly more easier to find but only give half the amount of Oricorio.
Sw/Sh: Route 10. Snom and Vannilish are the most frequent Spawn I could find for this stat.
S/V: West Province Area 2. Girafarig has a high Spawn chance between Porto Marinada and Colonnade Hollow. Can use sandwich to increase Spawn chance.
Hope this Helps.
