I'm not a guitarist now, but I do play the sax and the advice is pretty much the same when it comes to cases.
It very much depends what you're going to do with the guitar. If it's only going to be a matter of carrying it from house to car and back again, perhaps the odd lesson, maybe take it on holiday now and then, then a soft case/gig bag would be adequate. The best ones are padded, and it's really worth paying that little bit extra if you can afford it.
If, however, you plan on lots of gigging, in and out of vans, through airports, on and off coaches and tour buses, then you'd be advised to invest in a hard case - again, the best you can afford.
I think much also depends on what you've paid for the instrument and/or how much it's worth. If it was a very expensive pro-level model, then you're obviously going to want to give it a little more protection than an unknown brand you bought from a secondhand shop for a tenner.
Of course, if you buy a good quality case, you might be able to hang on to it when you upgrade to your next guitar.