Lugia is a great wall when not a level 10 Pokemon. It now has access to the ability Multiscale which allow it to take some of the biggest hits in the Metagame. In-Game it's just as good with it's Special Attack and access to STAB Aeroblast, psychic, Hydro Pump, and Roost for recovery, throw a Life Orb on that sucker and you're good to go. But seriously, Level 10 is where nothing is good unless you play LC.
Deoxys-S boasts the HIGHEST speed in the games. In competitive battling it works best as a lead, get some hazards up and screw the opponent with Trick, or use Taunt/Mirror Coat if up against a Forretress. IN-game it's probably not as good because of less than great attack stats and horrible defenses. In-game you'll probably prefer using Deoxys-A or Deoxys-Normal to do your bidding, the former because of large attack and good movepool, the latter because you may be a total noob and not know where to change the forms (I speak of myself here)
Pikachu: No, don't use it unless gimmicky or noob.
Metagross has some good typing and heck of an attack stat. It has access to some strong STABs, and is able to utilize several different items. He also has access to Hone Claws which makes for a good set-up sweeper. He's got some great Bulk and good Defense which allows him to take some hits well. I don't know why you compare him to Bronzong as they have entirely different functions (although they have the same typing and Bronzong can utilize Choice Band to some extent) past that Metagross can do far better with a larger offensive movepool.
Hope this clears some stuff up for you and if not comment, and I'll do my best to elucidate.