Both engines have essentially the same power potential- the difference in extra torque from the 300 comes from small changes in the injection pump, turbo, etc.
The big difference is an overall reduction in valvetrain noise on the 300. Land Rover went to great lengths to ensure that the only noise eminating from the 300 was bottom end. It sounds much more solid and less clattery. This does not relate to performance though, its just a NVH thing.
Personally I like the 200s... I have more experience with them. Both are bulletproof once reduced to the minimum of electrics. As pointed out, though, 200 stuff is getting hard to find.
The difference in the fan shrouds is due to the length of the bellhousing and the placement of the engine. The 200 has a very short bellhousing and the back of the motor is close to the firewall. The 300 has a very long bellhousing which places the front of the motor in essentially the same location as the front of a V8. If you want to split hairs, the 200 setup offers better weight distribution.
You can't go wrong with either if you know what to expect from a small displacement diesel. I know a lot of people who are disappointed from the "bottom end" performance of the Tdi's. Because they are small displacement, they rely heavily on boost to make the power they make. Once into boost and into their powerband, they pull like a freight train (especially after the right mods). But, idling in 1st gear off road, its still a 2.5L four cylinder. Just because its a Tdi does not mean it will idle over stuff like a Cummins 5.9. There just isnt the rotating mass and displacement.
Food for thought... Let me know if you have any other questions. Between my own first hand knowledge and the knowledge of those around me (whom I can point you towards for really technical questions) I should be able to help you out!
1972 Land Rover Series III 88"
2012 Jeep Grand Cherokee
2007 Suzuki DR650
The problem with forums is that there's too much "This is what I'm planning to do...." and not nearly enough "This is what I've done."