Well, I'm assuming that even though you got them from Fire Red, you are still somehow able to use them in later generation games, and somehow got it from that game. So, I'll give my opinion on these Pokemon you have now, and some suggestions.
Metagross
- Lax nature is not the best, but atleast it increases it's defense
- Some moves you have which are catergorized as special moves should be replaced with physical moves
Overall, this Metagross can still be worked around without having to catch a new one. Lax isn't the best nature since no nature that decreases a form of defense is worth it, but you might as well leave it as the Lax nature does increase defense. Metagross is also much better in physical attacks than special attacks, but it's unfortunate that no physical psychic moves existed yet, so consider replacing a special move like Hyper Beam with a physical-TM move such as Earthquake.
Alakazam
- Neutral natures aren't the best, but is always a good satisfactory nature
- Multiple psychic moves are not the best choice for a move pool
The Alakazam who have is ok in terms of nature, but I think you may want to consider changing an excessive psychic move, particularly Psybeam, in exchange with a TM such as Shadow Ball
Gardevoir
- Bold is not the best nature, but is still workable
- As said before, multiple psychic moves can be replaced with more variety
Gardevoir is a great Pokemon, and the nature does not alter anything positive, so it's alright. With the moves, you may consider replacing a weaker psychic move like Confusion with Magical Leaf or a TM.
Overall, each Pokemon is very different but each very good. I'm assuming your playing with these Pokemon in a game below Gen 6, so you don't quite have access to fairy-typed moves or a Gardevoir's secondary Fairy type. That being said, I do believe that your Metagross is your best choice right now as it has good defenses and attack. It alright is a high level and can probably beat majority of the Pokemon in the game anyways. The only suggestion, play around with some of its moves to get much more appropriate ones stat/type-wise.
*Please tell me if I have a detail wrong such as their possible moves learned or what game you have.
Hope I helped! :)
