Think bikedelivery is Paisley Freight. They do a service where they drop off the empty box one day and pick it up another which has helped me out a few times with sellers who don’t offer postage.
In terms of least clicks from search to parcel they are the most convenient. Last time I used them it was APC subcontracted who were great but it changes.
It really depends - if it’s low value and the postage cost detracts from this ironically it becomes more complicated/I have to really read the small print to keep within their weight/dimensions for the lowest price. For something higher value I don’t really think about it and just go for the best I can afford, consistently that has been Parcelforce here but it varies depending on local service I guess.
It’s all in the small print - I sent I garden tool to Ireland, inputted all of the dimensions and thought I was paying £16, in the end I paid £32 which wiped out the value of the sale as the small print stated they could surcharge if the item was oversize (in this case about 10cm of handle).
I’ve started to avoid eBay GSP entirely - last time I had 2 parcels for collection (clearly labelled with A4 printed labels) they then added their own labels. A £60 wheel rim ended up on the south coast UK with a buyer expecting a vintage garden spade - the garden spade ended up in the USA with the buyer wondering where his wheel rim was. No compo as the courier had tracking for both, I gave up trying to argue my case and wrote both off.