I can't really compare it with the other mentioned bikes, but the June before last I bought a Claud Butler Urban 100 for £200 and have spent the last year and a half riding to work and back on it - around 7 miles each way. I guess I must have done a little over 5000 miles on it so far. It's a little bit on the heavy side, but I enjoy riding it and it's served me well. I guess it could be said that having not ridden any other recent bikes (apart from a quick tryout at the bike shop) I may be riding a crap bike and just simply not know what I'm missing, but I've enjoyed the last year and half of riding, and I guess that's what counts.
Don't forget that there are several other things you may need to buy if you intent to ride to work every day; I would consider lights, a lock and mudguards essential, and although a lot of people use a backpack to carry their stuff around in, I much prefer having a rack and pannier as you end up much less sweaty.
At a quick guess (prices taken from SJS cycles):
A decent D-Lock with cable (that secures your front wheel): £30
Mudguards: £20
Basic Light Set: £15
Rear Rack: £10
Pannier: £30