There are plenty of guides on how to make a "best possible team." The best Pokémon, incidentally, aren't necessarily the ones with the highest stats. Mewtwo, of course, is near unbeatable, but some of the best Pokémon in the game (Jynx, for example) have actually pretty average stats, and some Pokémon with very high stats (Moltres, Dragonite) actually have a lot of trouble battling. Moves and type are important. You'll need a deeper knowledge of the game before you can make an ultimate team!
Here's a starting place, though, if you want to know which Pokémon are considered good: http://www.smogon.com/rb/tiers/ou
That list excludes Mewtwo and Mew as these Pokémon are usually banned in serious Pokémon battling. --- 'tobias xelkythe' anagrams to 'Sexy, bat-like, hot.' - ssbmdemon18 http://www.smashwiki.com/wiki/Main_Page
What is the team for? Battling friends? Competetive battling? In-game? Stadium? --- Not changing sig until I find 30 people who have read Iron Wok Jan. (and can prove it) 07/30 http://i2.photobucket.com/albums/y50/Tash12345/Gfaqs.jpg
In that case, swap out Gyrados for Starmie (Starmie is basically Gyrados with less physcial attack, better typing, STABed Psychic, and Recover).
Switch out Charizard for Zapdos. He's better.
Get rid of Machamp and replace him with Rhydon. He's your new physical attacker.
I think Slowbro would be a better choice than Alakazam.
Get Gengar out of there. He's useful in competitive play, but there are better choices outside of it. Maybe Executor or another physical attacker of some sort? --- Not changing sig until I find 30 people who have read Iron Wok Jan. (and can prove it) 07/30 http://i2.photobucket.com/albums/y50/Tash12345/Gfaqs.jpg
If you aren't going to be too serious about battling, your team should be fine. You might want to give Machamp the boot, and Gyarados and Charizard aren't good, but frankly your friends probably won't have anything much better unless they're competitive Pokémon battlers themselves. --- 'tobias xelkythe' anagrams to 'Sexy, bat-like, hot.' - ssbmdemon18 http://www.smashwiki.com/wiki/Main_Page