your decision is similar to mine, except that I was not particularly interested in multitracking as the first priority, but wanted the option too. The problem is, if you have a powerful enough computer already, do you spend money duplicating stuff with a hard disk recorder? Because I had laptops that were powerful enough for what I need an external soundcard made sense, there are guitar and microphone inputs as well as the keyboard and a digitech or external processor is easily hooked in. Look at the Edirol and Yamaha gear availble.
If you have a pc rather than a laptop you may want the hard disk recorder just for portability and not being fixed to the pc location.
There are many high end souncards to put in a pc to give you mixing and controller facilities.
The alternative to a hard disk is a mixer and recorder, dat, cd, minidisk, adat etc though mutitracking would not be so simple down this route.
It boils down to how much you want to spend and do you mind buying gear that duplicates what you can do in the pc, just for the portability.