If you want to play it safe go down the fluid path. Developing for fixed styles is more difficult (well for me I think it is) I'm speaking more of the design aspect of it but you can achieve some visually great looking styles going with a fixed width.
I've seen many designers go with fixed widths when there was no need for a fixed layout. And not to mention (my own opinion) more often than not fixed widths look absolutely awfull at low resolutions.
My best advice is go with a layout that will compliment your design/style. Never go with a specific layout if the design doesn't warrant that layout. I made the mistake of opting for a fixed layout when a fluid layout would have been the best choice.
As you can see
here. I opt for a fixed solution because of the header, I didn't want to have it repeating but came up with a solution with my upcoming style which has the same kind of header design except I opted for a fluid solution.
Anyway, Like I stated, go with a layout that will compliment your design the best and experiment there's always an alternative solution around the corner for every issue.