The 2.0 is a great engine - Can do big mileages with no real issues and is a LOT more reliable than the Mk3 TDCi. The 1.8 does seem a bit underpowered, and concensus seems to be that the 2.0 is a better bet.

The BMW, or VW equivalent is no more reliable, nor any less costly to fix if it does go wrong.

I've got a 2.0 TDCi TiT X and love it! For your 8K you'll get a good one, especially if you're not going for an Estate (which seem to hold their value better)