it all depends there is a massive ?? mark over the bitcoin mining compunity at the moment because no ones really sure when ASICs will be deliverd (if ever)
if you want to get onto mining right now go with something like a cheap ati HD5870, 5850 or ever 5830 these are now classed as budget mining cards
i use a couple 5870's putting out 700MH/s and they can also do others like litecoin
ASICS are only designed for bitcoin and sha256 currencys (theres a few but im not naming them all)
what i would personaly do if i was you would be invest in a cheap ASIC 5ghs (but odds are it wont be until late this year when you get it) and try to pick up a cheap older generation graphics card like i said anything from the 58** range is a pretty good deal right now. like i say theres alot of ?? over bitcoin mining if ASICs come out in the next month or 2 then GPUs will be very poor choice but if ASICs come out later then a GPU is a good choice
a 5870 for around $100 should pay its self off withing 2 months pretty easily aslong as ASICs dont get released
the ASICs if you get one early in the running will pay off withing 2-3 weeks but if your ordering now your looking at a payoff around 4-5 months depending how many ASICs get released if they do get released the 58** cards and a few later cards will still make a small profit for a while until it pretty much becomes an ASIC mining thing
BUT at the same time you could change the GPU over to litecoin (which isnt ASIC comatable) and make a fair amount of money off there
all in all you have 2 options
pre order ASIC and get a cheap 58** card for the time being ------this is what iv done
order a couple of GPUs and once mining on bitcoin isnt worth it change to litecoin