Most people have their prefrences. It depends what you need. In terms of defense, Golem is one of the best. In terms of attack, Steelix is one of the best.
I am pretty sure that boldore is not a legendary Pokemon
Jolteon.
Unfezant and swoobat
The three Legendary Bird Pokemon people refer to are Articuno, an Ice/Flying-type, Zapdos, an Electric/Flying-type, and Moltres, a Fire/Flying-type Pokemon. They are the first Legendary trio that was introduced in the original Pokemon Red and Green.
You can catch larvitar i Pokemon FireRed and Pokemon LeafGreen,but most people uses a gameshark.
The best legendary fire type is ho-oh. The best non-legendary fire type Pokemon is charizard.
I am pretty sure that boldore is not a legendary Pokemon
Best non-legendary water pokemon would be Gyarados. Best legendary water pokemon is Kyogre.
The best Rock Type Pokemon is Golem... I'm just taking a guess because I don't collect Rock Type Pokemon. But Golem CAN learn explosion, the best Pokemon move that does 250.
Jolteon.
A Rock/Fairy-type legendary Pokemon that you can only get through events. It was first introduced in Pokemon X and Y.
The best non legendary Pokemon, or the best Pokemon in general, is a matter of opinion that depends on your prefered type. Ask anyone and they will give you a different answer. However, the non legendary Pokemon with the highest attack is rampardos, who is not in emerald.
Normal type pokemon are best and rock type pokemon also.Electric attacks against rock type pokemon become ineffective.
Rayquaza is the best, but non-legendary is Salamence.
The strongest dragon type in pokemon Emerald, Sapphire and Ruby, is the legendary pokemon Rayquaza. In terms of non-legendary pokemon, both salamance and flygon are strong dragon types.
Unfezant and swoobat
Probably electivire or ampharos.