I know them all. had them all round to tea, and chatted with the lot of them.
at the weights that your talking about then i would say that they can all be good.
If its delicate glass/electronics etc - UPS (they won't carry more than 70kg consignments, most of the component suppliers use them. Most are lose loaders - which will put an small innocent box next to a freely moving crate that may way 100 times its weight.
If its not and its ruggid then TNT would probably be the best option.
Though worth checking out Amtrak, Interlink & its partners around Europe.
There are many others that some will recommend., but the most important thing to look at is the following.
1. Quantity of dispatches - # per month (get rates based on a months work - not per dispatch > you'll get robbed).
2. Delicacy of items - Style of courier (TNT is lose loader, UPS is max weight / compartment loader).
3. Quality of Service - Items getting damaged, getting lost, not getting there at all!
4. Type of Service - Timed delivery's, etc.
If you do get a courier in to chat about what they can do for you.
Ask about breakages, timed deliveries, coverage of the UK, whether they are a franchise chain, or entirely owned by the brand, how they pack, and the scalability of reducing their costs for an increase of work.
Royal Mail Special Deliveries are another option - though i would not recommend them for delicates.