Territory is still my favorite. There are a purpose to the battles and I don't feel like I have to be in a mad rush to help achieve them. I like when a battle ends up being drawn out and epic. This is the gamemode where I feel more like I am actually there at the scene and that is what I enjoy.
Countdown is interesting, but the constant start/stops/switching sides takes away from the actual battle in my opinion. Its harder to immerse myself into everything. I also feel like I am rushed to do things where I normally would be taking more time. Its not that it can't be fun because I have had fun at times, its just more inconsistent. Its a very clever gamemode that probably works for a lot of players, but between dying and the loading screens, there is too much downtime to enjoy it consistently.
Firefight is probably my least favorite at the moment, but at least with the way the spawn system works, players tend to stick together more. The lack of actual objectives and the very short rounds are what bother me the most. Things are over before you even know what is going on and when that happens, you spend more time with loading screens than actually playing the game. Its also the gamemode where I think most players are more out for themselves than working for/with the team.
Still, all the modes have their purpose and while I will prefer Territory most of the time, I can see myself playing the others occasionally.