I have been using Amazon Prime for many years now, and although I have had my fair share of issues ranging from fake items being sold to poor delivery estimates, Amazon's customer service, returns policy, efficiency, and systems are very good and have steadily improved over the years.
Most of my purchases (mainly electrical and electronic) are now from Amazon, with the more random and less dependable eBay coming in second. On many occasions I have surprisingly found Amazon prices, especially on new items, to be cheaper than on eBay, and there is no competition when it comes to customer service, with eBay being a bit of a joke if you expect a quick resolve when things go wrong.
Please note that I am referring to the Amazon Prime service that you have to pay a yearly subscription to use (about £79.00 at the time of writing this review). For me, the cost of this Prime membership is well worth it, but you will have to decide for yourself if this offers good value for money, as this will of course depend on your individual requirements, budget, and needs.
It would take something quite dramatic for me to stop using Amazon, but there's always room for improvements, hence the 4 rather than 5 stars.