I used Glasstec on reccomendation form Pistonheads. He did a good job in my opinion, didnt damage anything, knew how to take trim off an put it back on, used a cork/rubber block thingy at the bottom of the screen. that was 2 year ago, 2 winters later still no squeaking, leaking, etc.
http://www.glasstecauto.co.uk/
p.s. if yours is a heated windscreen, they may damage the conducting strips which go all the way round right next to the silicon seal that has to be cut through. May be a good idea to tell them to be careful or get a spare if you want to replace it with another heated screen. (I just went for non-heated so took the conducting strip out).