How are you at maintaining it yourself? If you want to, and want good reliability which you should be able to maintain fairly easily yourself (the engine) then go for the 300, the td5 will have to go into a garage for engine stuff. All the other bits are user-do-able, the td5 has lots of electrickery which doesn't like water being thrown at it - personally i'd go for the 300 for robustness but depends what you want it for!