I used to use TNT for business routinely, but then I found that they were constantly trying to screw me on price. I send quite a few parcels a week. They would agree a fixed price per consignment up to a specified weight, but then at the earliest opportunity jack it up once there was an established shipping pattern.
I would stop using them, they would call me with a deal to get the business back and the whole process would start again.

I'm now using Interlink. Apart from some small changes in fuel surcharges and deliveries to London congestion charge areas, they've stuck to the deal that was offered three years ago. Plus their online booking system is excellent. I'm not a shareholder or anything, I just think they are good.

( despite the fact that they are French

)