Easiest tier 3 solo raids?

Depends on movesets.

But Machamp is probably the easiest so start with him if you have some good psychic types.

https://pokemongo.gamepress.gg/q-a/can-you-solo-arcanine-gengar-or-alakazam

See my answer here

Depends on movesets and your strongest pokemon. Gengar is easiest for me because I have lots of Bite/Crunch Ttars.

I cannot for the life of me solo Arcanine...I blame it on lag and my phone which takes say, 5 seconds to use a potion, fainting on a boss raid and switching can take anywhere from 30-50 seconds...I also had overheat problems today that my phone was on "cool-down" mode today even though it wasn't even that hot.

I can do ~65 evolutions during a lucky egg while my wife can do ~90 (Iphone 7 Plus) without blinking or resorting to restarting tricks.

I think lag generally just makes everything slower so you are doing more like 20% less damage.

All my Golems are over the breakpoints and my Vap is maxed (39)...Also use Tyranitars in mid/low 30s range.

I can't wait to get a new phone and see if that helps...

I suppose I really should just use my wife's phone and login with my account on her phone (PTC account) and if it's instant win, then that's proof enough for me to just wait for now...

Generally, people say Machamp and Vap is the easiest...Hardest is Alakazam...Gengar depends if you have Tyranitar and Arcanine is a notch easier than Alakazam.

Flareon can be done with maxed Lvl 39/40 Golems and all the stars aligned with you launching your charge moves just before knockout and Jolteon is currently impossible.

For me:

Machamp
Gengar
Alakazam
Arcanine
Vaporeon
Jolt/Flareon- both impossible for me

Yeah, it depends on what you've got in your stable, vs. the moveset of that particular raid boss,...but for me (ranked easiest to hardest level 3 raids to solo):
7) Flareon
6) Vaporeon
5) Jolteon
4) Arcanine
3) Machamp
2) Gengar
1) Alakazam, (the hardest for me)