As a passenger, the B10BLE with Wright Renown bodywork. More specifically the ones that Blazefield got in 2001, the Y-HRN batch for Burnley & Pendle. As a regular traveler along the Mainline back then they were comfortable, quiet, rattle free, double glazed so you could always see outside whatever the weather and always seemed to be warm. The B7RLEs that replaced them weren't really any of those things. And the Versa's that replaced them... well...
Some of that original Y-HRN batch are still in service, just as comfortable and quiet as they were new, going on for 20 years pretty much continuous service out of the same depot. Although with only one interior refurb since new they're starting to show their age slightly inside. They're completely wasted on local town services now that they're mostly unsuitable for which is a shame.