The best squad leaders (at least as far as how they play as opposed to the brains of being a SL), either aggressive or not, are the ones that move a lot. If you are moving, the enemy is getting hit from different directions. If you are the type to sit far away from the flag and let your respawners fight in the same direction every single time, its just a matter of time before the defenders get wise, follow the trail of respawners, and kill the SL. You can still be far away and change the angle of attack.

Im personally pretty aggressive and i try to stay on the perimeter of the CP, constantly moving. Doing that means respawners come in from different directions and the enemy generally wont know who the SL is because respawners are seemingly coming from every direction. The only times i get on the flag itself is if the radius is huge or if everyone is dead and will be respawning. If everyone is dead, you might as well risk it and hope you live long enough for people to spawn, because if they do spawn, the flag will probably turn neutral quickly.

An important thing to do is to be passive-aggressive in your fighting. If you are fighting, be passive enough so that your medic doesnt have to risk his balls to revive you. But you can be aggressive in such a way that only the worst medics wont be able to revive you. Its important to try to place yourself in such a way that if you go down, the only reason you die is because your medic simply isnt doing his job. Be in a very easy to revive place, such as near cover or behind your squad members. If you get wounded surrounded by your squad, it should be an easy revive because whoever killed you is now occupied with the entire squad. If your medic says that he is dead, hide for 15 seconds till hes up and then resume being passive-aggressive. This is why when evillemon is in some of the more aggressive SL's squads that they say they dont have to worry about dying, because the SLs are fighting in such a way that a good medic, such as evil, can easily revive them when they die.