Easy to use, reliable and value for money.
I would definitely recommend you use Interparcel. Their site is easy to use and there is a great range of options to choose from that don't break the bank. You can even pay with PayPal which means if you're selling something on eBay, for example, you can use the postage money paid by your buyer. It's so easy to do and really reliable. I've never had a problem with using Interparcel and if I need a courier for any reason, they're the first people I go to.