For smaller parcels valued in the ££ hundreds, royal mail special delivery.
That is the only RM service where they can't leave something unattended on the doorstep, but have to leave a card and take it back to the depot. Tracking is good and the insurance is affordable.
Ordinary RM services, especially so called tracked 24 and 48 are no better than the cheapies and their tracking is a joke.
DPD is good but insurance cost is about 10% of high value items. Crazy !
Within the normal cover they are my preferred carrier.
Fedex and UPS can both be impressively useless. Avoid.
Evri can be fine if the delivery driver is good. Mine is, but I once used Evri for a rural delivery and the buyer caught them leaving the parcel 1/2 mile away ! Ask your buyers who they would recommend but make your own decision.
If it's a machine on a pallet, it will pass through multiple companies. You have no control over that. Bolt it down well, don't skimp on the industrial wrapping film and take many photos.
Have the seller photograph it before unwrapping just in case.
I only once encountered a buyer who dropped a machine getting it off the pallet, broke it and tried to blame the carrier / asked for a refund. His "explanation" didn't stand up to scrutiny so no.
Most folk are honest but do what you can to protect yourself against the shysters. Photos throughout the packaging process and make a photo record of weights. I pack very thoroughly and this works for me. I don't put a 10kg vice loose in an oversize box with 2 whisps of bubble pack like one shop I bought from recently....