I just put in a Milgard vinyl window last year and am very pleased. I know Anderson makes a good product but unless I was in an architectural situation that demanded a wood window, there is no way I would put myself through that kind of pain. Pella has a good vinyl window too, but my dealer said that they felt Milgard was the best operating and best sealed window. I can't comment on the relative performance of Pella v. Milgard, but I can say that the Milgard works beautifully. Vinyl windows are so smooth and easy in all seasons, that they're the way to go IMO.
Of course, the operation is highly dependant on the installation. Any window that is distorted - either racked or out of plane - on installation won't operate well. It has nothing to do with the window.
The other thing to consider regarding the installation is the flashing. Some installers just use silicone and call it good. IMO proper flashing is an absolute necessity. I installed my own and the flashing, while not hard, takes up most of the installation time. Caulking - even something good like the P&L polyurethane, may eventually separate. The leak will go unnoticed and you could end up with major structural water damage. Proper flashing (I think aluminum is best if possible) is more reliable. Also, a drip edge installed above the window if possible is well worth it.
Finally, when you say replacement windows.... some of these leave some of the old window in place. The inside of the window is removed, the frame is left in and the new window fits into the old frame. This is a common approach when replacing aluminum windows, but I don't know if it's done with wood windows. The problem with this is that the actual glass area get a little smaller. Personally, I don't like this kind of "replacement" window although the installation costs should be very low.