I have been really put off eBay (although to give eBay their dues it’s not entirely their fault). Buying and selling “stuff” was practically a hobby for me (mostly phones and camera gear) but I had a handful of shocking experiences last year with Royal Mail and actually ended up with 3 successful claims against them for late and lost items - but this was not without its headaches.Go whichever offers the most, avoid Ebay. Maybe CEX can offer something if you have one by you.
It of course doesn’t help that eBay is littered with <insert derogatory word here>…
Living in NI my options for sending expensive items is pretty much limited to RM so I’ve really dialled it back lately. In the future I will much prefer going down the recycling route (Music Magpie etc) where they provide the label and take responsibility etc.