Frankly, they all have thier failings...
Parcel2go are only agents, like comparethemarket, or Travelocity. I use them all the time, and have found that whilst their choice of shippers is patchy, Their customer service is excellent.
Avoid Yodel. I've used them, and had no issues at all. 48 hour delivery turned up 24 hours early. However, there are so many complaints about them online that it is an almost certain bet that they'll bugger it up next time I use them, so I won't risk it.
Hermes are also a shower of incompetent numptons. They didnt even bother picking up two parcels I tried to send recently, which is how I came to experience parcel2go's customer service.
Royal Mail / Parcelforce are ok ish, but two parcels I sent with them recently disappeared into the ether, only to turn up about a week later. They get the job done, but the recipient better be in or a journey to an out of town industrial estate to pick it up from the sorting office awaits.
For me, its TNT everytime.