Green.
I live in one of the safest Labour seats in the country. I'd be very surprised if UKIP had much support round here (inner SE London, extremely diverse ethnically and socially). If I lived in a marginal constituency I'd have to think harder about what to vote. As it is, I have to go with the party that most closely matches my values, and currently I think that's the Green party.
I used to vote Labour but haven't since the 1997 General Election. I had such high hopes after 18 years of the Tories and felt very let down by how they behaved once in government. Miliband seems a pleasant enough person but is not a convincing candidate for PM.
I don't vote Labour locally either because I don't think they do a particularly good job in my borough, but there again my vote doesn't make any difference. At the last council election we got a Labour mayor (he's been doing the job for 12 glorious years continuously), 53 Labour councillors and one Green councillor (not in my ward). No Tories, no LibDems, no Independents. Very unhealthy.