Assuming the horsebox your'e getting is on an old chasis, you need to ensure you can get spares for it easily. Our first horsebox was a leyland and thro needing to get bits replaced we became friendly with our local lorry scrapyard/mechanic!! On his advice when looking at a cargo and a daf, we went for the daf as he could easily get spares for them! I have a friend who has a Mercedes box and it drives very smoothly (she is however loaded, so unlike myself, doesn't have to go to the local scrap yard looking for spare parts when things go wrong with it, but drives it to a very expensive garage for them to sort out !!!)
I will ask OH when he gets in from work (wont be till gone 10) as he is a merc commercial technician! What sort of age were you thinking of? Might even push my luck and ask him to look at my car!
Have been told by my mechanic that mercs were heavier and bit more expensive for parts, daf and leyland were a better choice. Hence we didnt get a mercs.
When I was looking for a horsebox I was told that Mercedes are good lorries but their chassis are quite heavy so you lose some payload. Additionally that parts were quite expensive. I was advised to go with either DAF or Iveco as the parts are cheaper & readily available.
I have an 04 atego 815 they are a very good truck its good to drive , the downside is it has made my lorry about 300kg heavier than the man chassis that it replaced, so on that point if its maximum payload you need maybe not the best ! !reliabilty is second to none think of merc cars and the most of the parts are cheaper than iveco (Fiat) I would check the weight of what you are thinking of getting if thats ok then go for it.. I like working on and driving the daf LFs they are a very nice motor, parts however are pricey... Ivecos are well liked as a horsebox chassis but they are a bit cheap and nasty, and not that nice to work on!! think of a fiat car!!! oh and just one thing about Ategos the pre 2001 ones did sometimes suffer from electrical gremlins (dash board) but otherwise good..