What character is the strongest?

Being strongest... That's not enough information. Highest damage per hit, fastest dps, the range of the attack, and a myriad of other factors play in.
It not even about dps... if you simply aim to sawk a bishop for the duration of your 4th job i guess the big numbers and such might be important, but if you intend to actually play, versatility is where the real power lay. Being able to dish out the highest damage to mobs make you a mage, and their single target ability is mediocre. If you wan't huge damage on a single target, you are a BM or a NL, and loose out on strong mobbing. Avenger is usefull and not that weak, but it can't even begin to compete against say a polearmer DrK or a MM.
Personally I'd say Marksmen and Corsairs win as the most versatile characters, and ergo imo the most powerfull. HP is not even an issue if you don't crave to fight P bean. If so, heroes would be your best bet.

Look at the situation he posted.