Always loved Argos, and these days it's more reliable and linked up than ever, with their stock check, etc. They even have an app but the one time I tried it I found it to be clunky and very slow. I can't see any use for it at all considering that you can easily check stock on their site/mobile site - so why have an app as well?
Their staff are almost always very helpful and friendly (of course you're going to get exceptions - seeing as they're human beings, not robots). When I did have a problem - my payment would not go through - I called them and they even advised what I should tell my bank to get it resolved. I suspect all these "brain dead staff" are coming from those awful people who think anyone who works in a shop is beneath them - if you treat people with that much disrespect, why would you expect them to run around after you still?
The ONE criticism has to be when they have big reductions on items - you BETTER get in there quick, because whenever I've found out about the big reductions, they're out of stock EVERYWHERE. This can be very annoying - as you could accuse them of advertising something they cannot supply. So this knocks off the final star from me. But other than that you can't get much more legit or reliable than Argos.