Porygon-Z is worth it.
Porygon-Z is quite the good sweeper with an adaptability boosted STAB tri-attack/hyper beam. It has a nice movepool, and it’s speed is pretty good (though a choice scarf still might be good to have on it). Porygon-2 fulfills a VERY different role than Porygon-Z. It has great bulk that can be increased even more by an eviolite. It has reliable recovery in recover, and a nice movepool too. It is sometimes used to set Trick Room. It really depends on what you want.
As for In-Game, neither are accessible if you mean during a playthrough of it, and if you mean after you have beat the game, than Porygon-Z is definently better
As for Alakazam or cursola, Alakazam is DEFINENTLY the way to go. It’s special attack may not be as good as cursola’s, but it’s speed is far better. It has access to magic gaurd, which prevents weather damage, life orb damage, and status conditions damage which can prove to be very helpful. It’s movepool may not be the best, but it still is good enough. I would only use Cursola over Alakazam if you are using a trick room team. Corsola and Cursola are similar to Porygon2 and Z, as the pre evolution has great defense while the evolution is an attacker. So which do you want, an attacker, or a defender? Here are some movesets:
Porygon-Z@Choice Scarf/Life Orb
Ability:Adaptability
Nature:Timid
EVs:252 SpA / 252 Spe / 4 HP
•Hyper Beam/Tri Attack
•Psychic
•Thunderbolt
•Ice Beam
Trick-Room setter Porygon-2
Porygon2@Eviolite
Ability:Download/Trace
Nature:Relaxed
EVs:252 HP / 128 Def / 128 SpD
•Trick Room
•Tri-Attack
•Recover
•Psychic
Non trick room:
Porygon2@Eviolite
Ability:Trace/Download
Nature:Modest
EVs:252 HP / 128 Def / 128 SpD
•Tri-Attack
•Thunder Wave
•Recover
•Psychic
Alakazam@Life Orb
Ability:Magic Gaurd
Nature:Timid
EVs:252 SpA / 252 Spe / 4 HP
•Psychic
•Shadow Ball
•Energy Ball
•Focus Blast
And if you do want to use Cursola:
Cursola@Life Orb
Ability:Perish Body
Nature:Modest
EVs: 252 Spa / 252 HP / 4 Def
•Will-O-Wisp
•Hex
•Strength Sap
•Earth Power
Galarian Corsola@Eviolite
Ability:Cursed Body
Nature:Relaxed or Sassy
EVs: 252 HP / 128 Def / 128 SpD
•Strength Sap
•Will-O-Wisp
•Hex
•Night Shade
