Well, they all have problems with their couriers. By and large, you are probably best off with one that uses couriers that deliver efficiently in your locality.
And they all have problems with support, from time to time at least. Ebuyer went through a very bad patch but then employed more people, got on back of their backlog and haven't been too bad since. Refunds are pretty automatic too.
Again, only online contacts. But then, phone numbers tend to be expensive 0870 numbers that leave you waiting (ie paying) for ages before answering.