Both. 23 to 25, especially with a wider rim, is a big jump and the bike will feel much smoother. White industries hubs are great (I considered them before going King) and may well roll better than the stock Trek own-brand you had, especially if you didn't keep them serviced. Finally, depending on which wheel set you had, you likely have a different spoke pattern and possibly tension in the wheel, which can also impact the ride.

Be sure to keep up with servicing on the new hubs...