It probably depends which you can get your hands on at the right price, most of the Beech we get in the UK is European steamed (often German) which I used last time, 3” top, it didn’t move in the slightest and I was very happy with it indeed.
This time I’m in America and as Beech isn’t available I am using Ash, quite happily, and no I wouldn’t say it was a lightweight timber either, it’s all relative.
By coincidence a lot of the Ash we get in the UK is from the States anyway.
Or you could go mad and use both of course. Top and underframe,
Ian