dont get a megaflo, you pay more for a design flaw. Make sure whatever you buy has an external vessel(most have).
I've never come across a cylinder that had any issues really, apart from some of the older glass lined Aristons. The quality of some of the cheaper ones definitely isn't as good, but only in that the pipe connections are not always very straight, and the insulation casing is badly fitted. They work and don't leak just the same as something dearer.
I often use plumbe center own brand, they are well priced and made by heatrae sadia anyway, also used gledhill, kingspan, glowworm, range.