I am level 37 now, and have maxed (to 39):
Blissey ZH/DG 96%
Dragonite DT/O 96%
Next in line:
Machamp C/DP 100%
Rayquaza DT/O 96%
Tyranitar B/Cr 96%
Kyogre Wf/HP 98%
I have Mewtwo (PC/SB), Raikou and Zapdos all at L35, and I'm not planning to power any of them further. They are already serving me well at L35.
Besides Gengar, none of those pokemons in your list are worth maxing out tbh. Even then, Gengar is only useful in niche situations, or T3 solo raids.
Useful legends are Groudon, Kyogre, Rayquaza, Raikou. Optional are Moltres/Entei, Lugia, Latios, Zapdos.