The 1.8 litre version is far more modern and high-tech, I would definitely go with this. It is also reportedly much smoother (has balancer shafts, I believe). Plus it will fetch more money when you come to sell as it's a newer model.
But I wouldn't complain at the 2.3, though I would expect a discount. These are easily obtainable in the UK with our inflated prices, but you should still have some luck.
2.5-16v 1990 90,000m Astral Silver
2.0E 8v 1986 107,000m Black