I've owned a Series 2a 109", a series 3 109", a Lightweight, a 101, two 90's (I still drive one every day), a 110, and a Disco. On top of those, I've driven several Range Rovers, a Series 1 86",a series 2 88" and a Freelander.
In my opinion, the worst has to be the 2b Forward Control - ugly as sin, horribly underpowered and top heavy. Mind you, I've never driven one so I'm prepared to take that back if I ever do and it turns out to be a pleasant experience....
A close second has to be the petrol Mk 1 Freelander which has all the same problems listed above but they sold more of them so I'm assuming that more people like them.