If you enjoy attacking, then Romans would be a very strong choice. Their extra troop capacity can really pay off in close battles. Also the Roman Legion unique heavy infantry has more health than other heavy infantry, which should help keep your attack going longer.
The Japanese are more of a defensive nation, however the extra attack on their unique heavy infantry (Samurai) can help you destroy bases faster.
The Chinese are a well rounded nation, but aren’t particularly strong on offense. Their Chu Ko Nu unique ranged infantry are good for defeating defender infantry. They fire twice as fast, but deal 60% damage of other ranged infantry. However, you’ll still need other troops to mount a successful attack, as they are not as good at taking out buildings.
There are three other nations I’d recommend to you though – the French, the Germans, and the British.
The French unique heavy cavalry troop, the Chevalier, has more hit points than other heavy cavalry. The French also can train troops faster than other nations, meaning that they can attack more frequently.
The Germans have a good unique heavy infantry troop, the Vandal, but their real strength is in their faster refreshing Rally tactic that has a longer speed-up boost on it. This can often lead to getting in an extra 2-3 Rally commands a battle, which can be really useful for destroying strong defensive points like Catapults and Ballista Towers before they do too much damage to your army.
The British won’t help you win battles more than other nations, but if you’re in it for the loot, their 5% loot bonus from battles can really add up.