I don't like Push because, in some maps, when you attack there is a big wall of campers that won't let you do anything. And when you defend you are almost obligated to camp, which for me is very boring.
Firefight is not bad but the rounds are extremely fast. I mean, sometimes the round last less than 2 minutes.
Frontline is much better than Push but it sucks that you have to play it alongside with Push. It should be separated.
In my opinion, the best mode of all is Skirmish. Campers are few, you are constantly moving around the map, rounds last an interesting amount of time and it requires more team coordination.I don't understand why you removed this mode but is a shitty decision.
This game is the only thing I've been playing for months but with this change I won't be playing it until Skirmish returns or at least you separate Frontline from Push. I love this game but what a shame...
EDIT: with the 1.5 update the Frontline mode has been separated from Push. But Skirmish is still missing.