I always thought graphics was only thing nerds cared about... :\ I don't care for the art, I just care for the core game style. Halo is way better Bul, I mean, both have wierd things about them. Both blow up vehicles but in different ways. But in a way Halo has it tougher by letting me show you this:
Warthogs - in Halo 1 never show any signs of damage or can never blow up but the hardness of steering makes up for all of its psotives. It doesn't even show no signs of damage! Halo 2 has it tougher though as there are signs, they do blow up, but it steers way better. I always perfer driver though. This is mainly between... how you look at it. These are cars called 'Warthog' because of the horns in the front.
NOTE: In my case, Halo 2 has it harder, because you can auto-kill anything, expically Hunters! I don't think it could do that in 2...
Banshees - the flying vehicles of the Covenant - can blow up, even if you are in them. They show no signs of damage and auto-kill like the Warthog, if you can swipe the enemy with your wing, but its anonumous that Halo has it harder.
Ghosts - main transport by land of the Covenant - are more lethal in Halo 2. They can ram people over as they could not in Halo 1, but the circle engine to the left part is a deathwish to the driver if it is hit! Snipers get this advantage. However in Halo 1 they are deadly because you can die in them but the circle tank doesn't blow up - I can't confirm this because I haven't got it targeted in mutiplayer, as they take no damage AT ALL when no driver is in. Halo has it harder when you can only rely on your sole plasma cannons and you can very well blow up inside, while Halo 2 has it tougher by the tank explosion only. You can ram your enemys and get the boost for fast escapes when you can't in Halo 1 and the cannons too.
Scorpions - the big tanks that are unstoppable. Yes in both. As you can tell its hard for them to take damage in Halo 2 as they have very great defence but explode. Halo 2 still has it harder. I can guess that the timer is longer by a second in Halo but they can explode in 2... theres not much difference there... but a broken Scorpion possibility beats a 1 second rocket rate later can't beat the explosion possibility in Halo 2.
Now the possibilities of vehicles are tied, but hands down Halo 2 has it easier by the vast array of weapons Halo doesn't have. Energy Swords, Fuel Rod Cannons, Covenant Carbine, and DUEL WEILDING.
Its pretty obvious that Halo is harder... if you read this.