Can't say anything about a shuttle-shift since I've never played with one, but I did get to spend some time on a New Holland TC29D hydrostatic 4wd last summer. It was a very nice tractor ... very smooth, with no surprises. The trick with a hydro is to keep the fluid and filters changed. If you use the correct fluid, hydraulic filter, and change both according to the maintenance schedule, the hydrostat should last you for many years.
BTW, the Case IH and the New Holland Boomer tractors are basically the same thing, only with different sheetmetal and paint. The Boomers offer the SuperSteer front axle for a tighter turning radius; the SuperSteer is not available on the Case IH model, and I think the Boomer has one or two other features not available on the Case IH model. Other than that, they are more-or-less identical.