The Waitrose in this instance, better flavour and consistency, the Asda didn't caramalise well in the toaster (yes I like it that dark). To be fair, i have been using other brands like Sainsbo's quite happily, and (I think) even Asda's, too. This speaks more to consistency of quality than overall usability.
I've been very happy with Waitrose essential wholemeal, which is the same price as Sainsbo's too. Tesco (slightly cheaper) is OK, too, but I have suspicions about their consistency over time as well.