I use UPS via interparcel a fair bit and they both offer a decent service. My experience of couriers is that the cheapest often come with drawbacks wrt reliability / speed / general confidence.
Sometimes you can save on volumetric charges by repacking with smaller dimensions eg a German seller sent me the wrong intercooler but the dimensions of the double box were oversized and throwing out @£100 return charges so I chucked away the double box and it cost just £15. Fortunately there is also paypal returns scheme which reimburses return shipping charges.