If it has to be just one, has to be the full susser.
My 'one' is an old full suss and with the upgraded shocks with lock out it can turn into a rigid quicker than a teen watching Nigella licking a wooden spoon!
Sure it weighs a kilo more than a hardtail or two more than a fully rigid, but when you get onto the rough stuff all that is forgiven and forgotten.
Perhaps downgrading to a mid range full susser that is less nickable would sort the theft worries. It works for me.