Yet to have a pump failure since started using AIO liquid coolers. Oldest is 5yrs old?? and still going. Maybe I've talked it up now. Only used Corsair & Fractal Designs so can't comment on others reliability.
Be weary of those big air coolers if you're mounting it in a vertical case. I don't like all the extra strain it puts on the motherboard mounting points and will add some sort of support for it. You also need to be careful if you move your machine about. Try and do it with the cooler standing vertical to, again, reduce the strain on your mobo.