What Specialization(s) do you end up using the most or which do you prefer? And yes, you can “use” a Specialization (Tac Packs and Support Upgrades). I started my Specialization track with Pioneer. Why? It’ll make the mass grinding to rank up the rest of my Specializations a little easier without having to cause severe health problems in me from eating Doritos and drinking Mountain Dew for breakfast, lunch, and dinner for the 2XP 
you do know this question only applies to LE users.
the rest of us only have two specializations to choose from.
of the two i have, i prolly use them both equally. i use the wheelman more in BTB games and the stealth perk more in close quarters.
REALLY wish i could try out the other ones.