I work at the Nottingham branch at the moment and would say go for JL. Trust me we will pick up all repair costs for any hardware failures, (not accidental damage unless you extend, but home contents and/or travel insurance covers that usually). If they total over 50% of the original value of the goods, we ask you to reselect a new item for the remainder of the guarantee, (although since year one is Apple and year two is JL, if you are within year two even by a week, you get a whole new year from Apple anyway as it is a new serial number). The same applies to a lesser extent with extended warranties up to 5 years, (although we don't deal with the machine and repair costs, the insurance company who you take out the extension with will).
If you sell it on, make sure you give them the receipt too as they will roll over to any new owner.
As for 28 days no quibble, I don't know where that phrase came from, but it isn't quite as straightforward as that. If you have opened it and changed your mind, sorry but it's a minus 10% refund, (we pass on costs to you rather than markdown by 10% and lose cash for others' indecision). If it is faulty, we check it out first, (as manufacturers will do the same and if they turn out not to be faulty, we have them returned to us, have to mark them down and lose cash), but if it is genuinely faulty we will exchange. For dead pixels, we don't have to exchange unless there is one dead centre, 4 within 1cm of each other or 7 around the perimeter, but more often than not we do as a gesture of good will
On the whole, buy from JL and you won't get better service elsewhere I guarantee you. Even if you don't feel like you are getting good service at times, I assure you other retailers would do even less for you.
if you think you're going to keep it (or give it to someone you know) in that time.