All the classes have strengths. But the one I always seem to drift by was the engineer.
I love the shotgun....A LOT.
And I mean, even long range you have high chances of hitting at least SOMETHING.
I don't detpack spam/dispenser spam much though.
When I use sniper, I normally go point-blank range sniping, its real fun! (at least, against bots, havent tried online) I somehow can always hit even when no crosshair is present(in fact, in some mods where the sniperrifle has a crosshair i get disorientated

) Hiding while sniping? Pfft, i can do that, its also effective, but I prefer going around being crazy and point-blank/one-hit-kill people.
The scout is also the fastest unit too.
The heavy, well, I love to rocket enemy units, try to get at least 2 bots with a rocket. But I prefer suicide-mining a bit more. Drop a mine on something really strong (i.e. vehicle, large grp of enemies)
The rifleman is well balanced, and I respect that. I also love the fact they have FOUR thermal detonators, wow I love being a mad grenadier.
I don't really like the commander classes, nor the specials, they seem, missing something, or not to powerful on a certain field I like.
All in all, most of the base classes have a place inside for me. Cant really decide a fav.