Personally, the most comfiest e-leather seat I've been on is on the MAX X14 Omni's, about three hours and it felt like I was sat on a bed with headrests. The '57 X15 E400s aren't far behind.

There is a difference in the '57 and '14 Sapphire E400s though. The older, has firmer seats, not nice if traveling beyond Bedlington from Newcastle. The newer buses have softer seats, even on the first day of service, they're much better now (love the downstairs rear seats!).

The MAX X10/X11 Gemini seats are OK, not far behind '57 Sapphires, the MAX X12s were ok too.

The MAX X18 E400s are also nice to sit on, but e-leather on a long journey like this is not recommended.