My favorite map was The Pit because it had fun, balanced gameplay. It played great for standard gametypes, but at the same time worked with gametypes like team rockets and such. It also had a good mix of long / short range encounters and plenty of options for manueverability. aaah, I remember playing good ol' team hammers on that map...
Valhalla, a mix of that good old fasioned Blood Gulch Gameplay, outstanding aesthetics, and some great vehicular destruction, which as you can probably tell by my gamertag, I enjoy.
Definitely Valhalla. It brings back tons of memories. Don't forget Sandbox. That there map gave us Forge.
My favourite map is Sandbox. It is my favourite because it combined vehicle gameplay and infantry gameplay close to flawlessly while still providing an open environment. Along with the easy forging and the design of the bases.
Valhalla FTW! I remember the days where me and my friends would go full charge mode on the enemy, the fear in their faces when they heard us approaching, the roar of a hog flying over your head, then a sniper bullet, and the words 'Flag Recovered'. Ah, sweet nostalgia. Oh, and Snowbound, but that's because me and my friend would troll people through the shield doors. Shotty and tbagging on one side, sneaky sword ninja and unsuspecting victim on the other.
Rat's Nest and Construct rock. But I can't really choose: I really like Sandtrap, Valhalla and Standoff as well, and Guardian and The Pit are also great maps. I also love Ghost Town for the extraordinary aesthetics. And if 343i ever needs Invasion maps, then I suggest they take a close look at Last Resort and Highground. Those maps are great as well and I really wonder what they would be like for Invasion, if tweaked a little.
Ghost Town. Didn't really like the Map itself but Forge Variants were epic. Treehouses, Racing, Infection...
I'd say Avalanche. I loved the base design and the struggles for holding the bottleneck. I think it is one of the most beautiful maps, as well.