The advantage of baize cloth over felt is that baize is a tightly woven cloth rather than compressed together. It is therefore much thinner and goes over lumps (hills) better - even quite big lumps. Because the cloth is high quality (95% Merino wool) when you come to remove the lumps, even after a few weeks, the cloth goes flat again - it hasn't stretched. I always found that felt stretched, gradually moulding itself to the shape of previous lumps and wasn't able to be a basically flat surface any more - not a massive problem but, I didn't like it.
I use my cloth downside up. It is rougher and appears more 'grassy'. The 'grassyness' is the advantage. The disadvantage is that it probably doesn't hold the paint as well as the other side might (just guessing here) and the cloth needs to be resprayed periodically.
I've used all kinds of 'base terrain' in the past but this is the best all round solution I've found. All I need now is a beige one for desert terrain.