I'm not a fanatic, but I highly respect Williams. One of the teams that aren't in formula one to sell a product, but instead in F1 for the love of racing in F1. A real battling team.
Generally I'm more of a driver fan, I'm barracking on Ferrari this year due to Raikkonen (I never liked Schumacher). I like the driver lineup for McLaren this year also.
My favourite F1 team ever (based purely on the F1 cars they made) would have to be Lotus. Very innovative, bold designs and also produced some of the most beautiful cars ever in F1.