I gave up with Parcel2go some 3 years ago over an unpaid insurance claim compounded by poor service from DHL. They didn't pick up or deliver unless they had something else in the area to make it worth their while. I don't mind waiting in for a collection to take place on the date specified but if they don't turn up...............!
I used UK Mail for UK deliveries for some time but they got a bit expensive, especially when they started charging a lot for redeliveries.
I have used UPS via the www.Interparcel.com website for some time now for both UK and overseas deliveries. They have proved ultra reliable and reasonable cost. The insurance is handled by Interparcel and so far they have been very fair. UPS lost a pair of Beolab 6000's going to Spain and damaged a BC9500 en-route to Portugal. On both occasions I was paid in full for my costs. There was another instance, can't remember the details but I was also suitably compensated.
One thing I would point out is that the whole insurance claim does take some time and they will ONLY deal with their client i.e. you! Because of the time that will be taken, you will need to take it on the chin and replace the item or reimburse the buyer promptly. Then argue your insurance case with the courier. You may not like it but that's the way it works best, in my experience.