Heads/Cam at the Same Time vs. Separate
You don't have to worry about dropping lifters. You can replace them if they're worn. You also have a lot more space to work.
I just found it alot easier doing H/C than when I did a cam alone.
Then I didn't heads/cam on my car with 1 other friend. We spent about 31 hours on it over a 3 day weekend. I didn't disconnect the AC or the fuel lines/intake. The cam swap was definately easier.
When you do heads/cam, you'll probably want to do other things at the same time, like:
pulley
double roller timing chain
ported oil pump
these add to the expense. TSP hooked me up with a great package price for heads/cam/pump/pulley/chain/blah blah blah - every bolt and gasket needed. Cost between $3-4k with a SPEC clutch and alum flywheel, linelock, etc.
You can pull of doing a cam swap for much cheaper, but doing the springs will suck. That is about half of the time right there. But, like was said above, you will have to duplicate much of that work when you want to add heads.
FWIW, the stock heads are pretty decent...if money is an issue, either do a cam only (LS6 cam/springs are dirt cheap), or wait til it isn't.
Once you start feeding the mod monster, you will be stuck in a neverending pit of costly upgrades

