I have used Orange, Vodafone, T-mobile, O2, BTCellnet, Virgin over the years and now back with Orange on a Dolphin contract (£35 month). The reason is I get unlimited texts, 500 anytime any network minutes a month, but the real reason, I get 8mb broadband for only £5 month extra and this also gives you free phone calls via your broadband router (just plug a spare phone into it) to over 100 countries. Just email the room number for your hotel to your home and they can ring you free for as long as you want. Used it to call UK, Norway, USA so far and all free for hours of calls. No problem with call quality etc.
Just worth considering.