I have done either/or-sparging both on HP 1050s and old Waters(600 series) instruments, and vacuum on the HP/Agilent 1100 and on the PE 200s I have now and detest. I've never done both.
My experience with sparging has been poor-it uses a lot of helium(which isn't exactly cheap these days) and in my experience doesn't always do the best job of degassing. IIRC, I did like the implementation somewhat better on the Waters 600 than I did on the HP 1050-if I'm remembering right the Waters actually let you set a flow rate in the menus and keep it somewhat consistent, while the 1050 just gave you four knobs across the front of the solvent tray and you set them until it looked "about right." Even sparging both at low and high flow rates, though, I'd still get occasional bubbles. When I was running a 1050 daily(which I used a lot more than the Waters 600, even though the HP/Agilent fanboy in me has to acknowledge the Waters as overall a better unit), I'd usually drop the solvent bottles in the ultrasonic bath and stopper them while connected to house vac to do gross degassing before loading them up in the solvent tray, and then just sparge for "maintenance."
By contrast, the in-line vacuum degassers I've used just work, and work well enough that I forget they're even there. My PE 200s are used infrequently these days, and when I first power one on I generally spend a few minutes chasing out bubbles just in the process of getting things primed. Once I've spent a few minutes doing that, the systems will run days at a time without the slightest worry about bubbles. I'll only see one if I dally in solvent refills and let solvent evaporate out of the frit/start of the line. In fact, the degasser is the single most trouble-free part of the otherwise miserable Perkin Elmer HPLCs