I wanted to try and help, so here are my preferences for wishforge farming/evolving. These choices are based on a few different things, such as
-if you want to hatch and evolve the pokemon yourself
-if you want to collect pokemon from the shelter (depends how plentiful the pokemon are)
-if you want to grind for specific type gems while also hatching pokemon to evolve for wishforge
It's a long post so I hid everything in a hidebox:
Reasoning: Low EHP needed to hatch, low evolution requirement (level 15)
*Azurill or Igglybuff are also good choices, as they have low EHP and only require happiness to evolve. However, if you want to farm normal gems while also producing normal-type RTE, stick to Sentret, because Azurill and Igglybuff are 1/2 fairy type. They won't always give you normal gems. Also, Azurill requires one of the parents to hold an incense when breeding, in order to produce Azurill and not Marill.
Fire: Cyndaquil or Chimchar (although most fire starters will work just fine)
Reasoning: All the fire-type starters evolve relatively quickly, but if you want to be specific, the two listed only need level 14 to evolve into their 2nd stage, versus level 16 or 17 for some of the other starters.
Reasoning: Super quick to hatch and evolve at level 20, so they're pretty good for wishforge.
*You could also use Azurill for water type RTE, if you prefer. They do not give water gems when you hatch them, but will credit water-type wishforge when they evolve into Marill. Azurill also tend to be plentiful in the shelter.
Reasoning: Low EHP, only needs happiness to evolve.
Reasoning: Low EHP, evolves relatively quickly at level 14.
*A really good alternative is Eevee/Leafeon, which only require you to place an eevee in a grass-type field, and they evolve instantly. This is a better option if you have a good shelter pass, and when eevee are plentiful in the shelter.
Ice: Vanillite or Spheal
Reasoning: This is a tougher one. Vanillite, Snorunt and Cubchoo are the only 100% Ice Type pokemon that evolve, so if you are specifically grinding for ice gems, these are your options. Vanillite, IMO, would be easiest to evolve due to the level requirement. However, If you do not care about occasionally getting different type gems than ice, Spheal would be, IMO, a better choice.
*If you ONLY need the RTE aspect, go for Glaceon, which evolves from Eevee when placed in an ice-type field.
Fighting: Crabrawler or Riolu
Reasoning: 100% fighting type, so you ONLY get fighting gems. Crawbrawler evolves instantly when placed in an ice field; Riolu evolves with happiness.
Reasoning: 100% Poison type so you ONLY get poison gems, evolves at level 16.
*Weedle is a very good alternative for RTE, as it evolves very quickly. They are 1/2 bug type though, so if you want to hatch them yourself, you won't get entirely poison gems. For an easy, passive alternative to RTE, try Budew, which requires only happiness during the day time.
Reasoning: 100% ground type, evolves at level 22.
*Wooper evolves slightly faster at level 20, but is 1/2 water type, meaning you will also get water gems if you hatch them yourself.
Flying: Situational, but probably Woobat
Reasoning: The majority of flying-types are 1/2 flying, 1/2 something else, so you will have to deal with getting a different kind of gem some of the time. Because of this, I recommend farming two badges at once! If you are farming flying badge, choose a pokemon with 1/2 flying and 1/2 of whatever other type you want to farm! Most flying types evolve relatively easily; Woobat evolves with happiness.
Psychic: Abra or Woobat
Reasoning: Abra is 100% Psychic type and evolves at level 16. Woobat is 1/2 Psychic type but only needs happiness to evolve, and also has a lower EHP than Abra. So it's up to your preference!
*Espeon is great too, if you just want the RTE and don't want to hatch. Eevee are plentiful in the shelter, and evolve into Espeon during the daytime with happiness.
Bug: Caterpie or Wurmple
Reasoning: Pretty easy; they are 100% bug type, low EHP and evolve twice, at level 7 and level 10.
Reasoning: 100% rock, and evolves into Probopass when placed in an electric type field.
Ghost: Shuppet, Duskull or Gastly
Reasoning: Shuppet and Duskull are 100% ghost type, but evolve at level 37. Gastly is easier to evolve at level 25, but is dual-type, so you won't always get ghost gems.
Dragon: Bagon or Gible
Reasoning: Bagon is 100% dragon type, and evolves twice at, level 30 and 50. Gible evolves faster at level 24, but is dual-type.
Reasoning: Low EHP, 100% dark type, evolves at level 18.
*Umbreon is better if you just want the evolutions. Evolves at night time with happiness.
Steel: Nosepass or Klink
Reasoning: Nosepass evolves into Probopass (which is part steel type) when placed in an electric field. However, Nosepass does not yield steel gems when hatched. If you want only steel gems, Klink is the only 100% steel-type that evolves, at level 38.
Fairy: Cleffa or Togepi
Reasoning: Low EHP, 100% fairy type, and evolve with happiness.