Don't get me wrong I like the D-Day game but out of all the times I have played it I have never seen the allies win. It has to be the most unbalanced game in the A&A group.
When you have played DDay, have you played with/without the tactics & strategy cards? Has that affected much?
I have had the allies win in DDay; think the learning curve is a bit higher for them like in Bulge.
another aspect to consider might be how many players you are gonna have play often--these 3 games are only up to 3 players, GC & BOTB being only two players. DDay lets you add a 3rd player.