I'll give you my perspective, as I have both an 03 X, and a 2013 Frontier Pro-4x.
I will 100% agree with
@Prime. The second gens make a better daily rig. They are bigger, have a bit more room, and WAY more power. They do not, however, get much better gas mileage.
For wheeling, while my truck has a rear locker, I'd take the the first Gen over the second. You would be very hard pressed to break anything under a first Gen. I've had mine for two years now, and beat the snot out of it in the Oregon desert, and the only thing I've had to fix is wheel bearings and the centerlink.
I have no lift, no skid plates, no aftermarket front bumper.
I will NEVER get rid of it. I might SAS it at some point though.