Oddly, both my choices from from Alexander. First up is the pre MMC The Enviro 200. The earlier the vehicle, the utter worse they are. There seemed to be something around 2006 where the quality dropped on the late build Darts, and didn't pick up in the early Enviro 200s. My local currently has a 54 plate Dart (a perfect, smooth and very reliable machine), a 56 plate dart (vibrates a lot when idle, radiator stuck on permanently) and some of Stagecoach's 07, 58 & 61 plate Enviro 200s. They rattle like mad, shake a lot, often some of the least reliable vehicles around. My heart sinks when I see one of those turn up on my local route, or find their way to a long distance route like Basingstoke > Andover / Newbury / Alton & Liphook.
My second choice is the ALX 200. Basingstoke seemed to end up with the runt of the batch, mostly ex London examples which had their centre doors removed. They rattled like mad, often leaked, and for some reason a number seemed to have something akin to ballbearings rattling around In the roof which made every journey even more irritating. Unfortunately for the good people of East Devon, a number ended up down in Exeter / Exmouth for several years later - which made me laugh seeing Line 5 branding '
North Hants Hospital * West Popley * Oakridge * South View * Town Centre * Buckskin * Hatch Warren' turning up on the 57!