I've bought a lot from Thompson & Morgan. Couple of reasons: 1. I had a code that let me repeatedly get free P&P 2. Their customer service is excellent.
I have had a few problems with them, but one email to let them know and I've been immediately refunded or had replacements sent out.
I received the wrong bare variety of hardy geranium. As they were bare root I didn't realise for months. T&M sent out replacements as soon as I contacted them. Only downside was this was much further through the season so I lost some 'growth'.
I had one plant mislabelled. Turned out it was the right plant but I couldn't be sure at the time. Contacted them, again they sent a replacement immediately.
I had 3 of a 9 jumbo plug collection die within a week. Those 3 were all the same variety so I didn't think it was a me problem. They couldn't replace as out of stock so they refunded the entire collection.
And I think in the early days I had a hydrangea that looked like it wouldn't survive. I got in touch, they sent a replacement. I planted the sad looking thing anyway and it pulled it's socks up and is still going.
So yes, problems but excellent customer service.
I have also had plants from Farmer Gracy (and am expecting more soon). I was lured by sales on bare roots + free delivery. The plants are only a year old and all grew reasonably well. But that was just last year so I'm hoping they push on a bit this year.
I was decidedly unimpressed by Sarah Ravens packaging and was survived the plants survived the journey. But to be fair they did all do well after planting.
I have quite a basketful waiting to click go on at J Parkers. Seem to be good value and they have a Jacobs ladder that I can't find anywhere else. Can't speak to quality or customer service yet.