Which one to Max

Charizard:
Blast Burn trumps Overheat by a mile. Move set should always be prioritized over IVs, especially in cases where an ideal move is no longer obtainable. Go with the Blast Burn one.

Gengar:
Again, Lick is superior to Hex and Sucker Punch. I personally would have maxed the 93% one first but since your 91% Lick Gengar is already 10 levels higher I'd go that route instead. Alternatively, keep it at L35 and power up the 93% one to L35 as well. The cost from 35 to 40 is stupid expensive for the low gains whereas bringing the second to L35 will see more immediate benefits.

I wouldn't max a charizard at all, but if you must, blast burn is the only one worth considering.

For gengar, your level 35 is okay as is, but if it needs some levels for a break point in lick, go for it then.

Your priority for maxing should be machamp, Shadow ball Mewtwo, etc...

For Charizard, i choose the Blast Burn. But your OH is not bad, its already in a high level anyway. I wont do anything for both of them yet, i wait till there be a good counter for raid bosses again.

For Gengar, if you need it as backup for your dragon squad or your dragon squad is not strong yet,you can powerup another one lick Gengar.

Depend on another counter that you have, in this case i make Giratina as an example that should be enough if you can play with many trainers if you only have 3,4,5 trainer to raid, then it depend on your other counter and off course another trainer squad.

If you are not raiding in Time Attack Mode all the time, or a really hard mode like duo or trio some T5,a level 35 Pokemons is more than enough. You can max it if you want or like it off course
I am not taking last breakpoint anymore as a determining factor in poweing up because it depend on what raid boss you raid against.
I ussually set my counter for 5 man a legendaries raid now, not as hard as a hardcore mode, but still fun and give decent challenge for it.
I use stardust as a meassure, easier than using level that not shown in the game (it is also easier to explain to casual or trainers that dont read forum like this gamepress or reddit). Ussually pokemons that is a good counter for a raid boss can do well in range of 5000-8000 stardust for 3-5 man legendary raid.
Sometimes you need to max it out if you have to carry your team mates ( with many new and returning player, it happen to me)

If you have just reached level 38, focus on maxing out the following first before you consider Charizard and Gengar:

1. Machamp with Counter + Dynamic Punch
2. Tyranitar with Bite + Crunch
3. Blissey with Zen Headbutt + Dazzling Gleam
4. Metagross with Bullet Punch + Meteor Mash (if you have one)
5. Dragonite with Dragon Tail + Outrage