Ranking all current d/g max pokemon based on their usability and future usability
I would love to share some of my research:
Safe g/dmax investiments (legendaries are out):
Excadrill (God tier) It can fight againts half of the gmax pokémon, dealing damage and tanking. Sometimes both. It has everthing: amazing moves(mud shot and metal claw), amazing typing (a bunch of resistences) and amazing stats. I would recomend at least 2 with ALL Max moves Power up.
Gengar (S tier): good typing, amazing moves (shadow claw and sucker punch) and amazing stats (a bunch of attack). This is a pretty solid one. It is usable as a tank for Future machamp,snorlax,urshifu. Cuz of his high attack stats deals big damage and has a gmax form. I would recomend 1-2, one being a gmax one at least. It can be build with Shield and attack maxed out.
Blastoise (A+ tier): amazing tank for ALL fire and water gmaxs. Build 2 (does not metter If It is g or d Max. Max out Shields at least.
Rillaboom and inteleon (A+ tier): Both are the best attacker for their types as gmax, and rillaboom Works as a tank. Build 1-2 (at least 1 gmax). Just build 2 If you need them and the gmax was not obtainable.
Charizard and Venu(A-): Both are great as tank for grass(venu is better by Far[more bulk and dont need and elite fast tm]) and water (Venu only). Both are great as attackers (gmax forms), but they are not the best. Build 1-2, at least one gmax for Zard. Venu = Max Shield, maybe Max attack (gmax only). Same for Zard.
Machamp and toxtricity(A-) : Amazing dps ones as gmax and dmax. But there are other options (not against snorlax and Eevee). Max out only their Max attack. Both are bad as tanks (type, stats and the lack of 0,5 s fast moves).
Metagross (A-): It is Very strong, but not that strong. Very good typing. Very good stats. Lack of 0,5s fast moves (yeah It metters this much). It is a amazing ALL rounder, can tank moves and deals a Lot of damage as psychic and steel(outclassed by excadrill's metal claw). But still great, build one, ALL Max moves maxed out (Max attack->shield->cure). Lets pray that Niantic gives It metal claw, It would turn easily into a S tier.
ALL others already realeased are meh...Cinder is waiting for his gmax, until there... Zard flying/fire is the king, tanking and dealing damage.
Future amazing mons (not counting the gmax):
Magnezone (probably god tier): Type? Stats? Moves? It has everthing!
Almost ALL the pseudo legendaries(S tier): Good Type. Amazing stats and moves.
THIS RANK WAS MADE CONSIDERING THE MAIN GOAL AS DEFEAT GMAX BOSSES. SO,USEFULLNESS OF THOSE POKÉMON ARE ESTIMATED BASED ON HOW GOOD THEY ARE AGGAINTS ALL GMAX. EXCADRILL IS A GOD TIER CUZ IT CAN BE GOOD AGAINST ALMOST HALF GMAX.