crate engine

My 2004 Partner 1.9D has a bad engine. I'd like to get your opinion on a few things. It's already bad. It's going to be 40-50 anyway. Instead of spending that money on it, would it be better to buy a used one? There's also the issue of the engine already gone. I'm thinking of getting a 2.00 HDi instead of a 1.9 and getting it installed. It'll at least be faster and consume less fuel. Which one do you think would be more logical? Frankly, I don't know anything about such matters.