I am in a bit of a political wilderness at the moment too. I can't see any benefit in having any of the parties' leaders as PM. I wouldn't feel reassured with any of them in the role.
However, I think as a whole, we have a tendency to fail to separate the party leaders from the party. We are not voting for the Prime Minister, but for the party we want to govern.
The politicians won't be in place forever, but the parties (mostly) will go on, so it's the party politics that we should be voting for, and not the person who will live in 10 Downing Street.
There are bits of each party's policies I like, but none of them have enough bits I like to make me want to vote for them.
I am in a real dilemma over where to place my X on 12th December. (That said, living in a Conservative stronghold, albeit one with a very good MP, it won't make a jot of difference which way I vote.)