I just buy Vodafone, but that's because they have a shop at the airport for me to go to while waiting for my transfer.
PS: Also, if you have any experience to share of visiting prague, i am traveling alone
I'm not a fan of Prague myself. The place is very touristy and the locals seem to resent that. We tend to fly in, have a day there and then head to other towns first thing the next morning. Personally I could happily give the place a complete miss and get the train the same day as flying in but the Mrs loves a restaurant in Prague (Cestr, stunningly good beef) and always wants to walk over Charles bridge (God only knows why: it's always packed with people). My top tip is to dive down random streets just to see what's there and keep off the main tourist runs. Oh, and don't bother trying Absinthe: it's hugely overpriced and something no self-respecting Czech would do anything other than laugh at (or sell at vastly inflated prices to gullible tourists).
One of the few places I have found where locals happily mix with tourists is U Zlateho Tygra (the Golden Tiger). Awesomely good beer and the crowd really do not give a fcuk who you are or where you're from. The first time we were there, a couple of years ago, we were sharing a table with two elderly Spanish tourists who were happily talking to a Czech couple they'd just met in Russian about poetry, two Czech blokes who appeared to have just finished painting a flat, three middle-aged Czech blokes who spoke some English and a smattering of Polish and the Czech deputy foreign minister and his assistant (or so one of the three middle-aged Czech told me, I didn't believe them until later when I googled the bloke and found they were either telling the truth or the man had a twin brother). Don't miss the place.