I've been with BigCommerce for many years now and am very pleased. Their tech support is prompt, their platform is stable, their website and admin back end as a whole is very efficient and good value for money. I came from a WordPress cart, good God never again - don't touch them with a barge pole, so BigCommerce were a dream after that nightmare. My only grumble is there are lots of small things that could be improved but despite their town halls and forums, it takes a while for customer suggestions to be implemented, if they are taken up at all. My one complaint is when you choose and add "you can also buy this" products to up-sell from another product, the site shows you products that are out of stock, and you could unwittingly attach them if you don't realise they are out of stock. This is a pretty simple and obvious error IMO and I wish they'd address it as I sell hundreds of products and don't always know which ones have gone out of stock! I raised this on their forum and heard northing back :(
