t-mobile - cheaper, better deal (12 months full monty for £16 with £50 cashback) and I do get a stronger signal where I am. Dreadful customer service though which is based in India or similar.
not from my experience.... I've not had an english sounding person yet, they've all had the 'indian call centre accent' with 'english' names (we can't tellI've only ever had excellent customer service from T-Mobile in the past (before I left yonks ago, then I returned a couple of years ago and were great. Not needed to access cust service recently and from what I remember their cust service centre is UK based.
Am tempted to call them up about he speed cap as I'm sure I could do with the extra speed on my HTC One! Is it literally just a case of asking an operator about speed caps and removing them?
Your download speed will be capped to 4mbps but you can use as much data as you want without worrying. I found my data speeds on o2 to be slower overall but more consistent, with t-mobile it can be very slow at times and very fast at other times.