Soldato
I Also find duos easier than squads if I can be bothered to play it as it's boring. Solos is just life sucking.
I tend to agree regarding solos in that I find it really hard to pluck up the motivation to start a game, but once I'm into it and progressing towards the last 20 or so I find myself totally engrossed, more so than squads, its pretty intense because nobody is there to rescue you or back you up.
I think the teamwork is better in duos as there are only two of you, squads can be a bit more frustrating in that respect as your team mates tend to care less about the value of your life. If one person gets killed in duos that's half your effective fighting force gone, with squads, people tend to shrug a bit more as its only a quarter lost.