In terms of scenario design I don't think there is much to choose between them. DBP can definitely be a slog, some of the scenarios are a bit on the large side for my liking, ToD I would say has probably given me more hours of fun than any. But then there's Vietnam... and the great thing with Vietnam is that you then have access to the excellent IronX mod, "Red Star over Europe" In my opinion, probably the best mod produced for the SB series.
So...looks like you just need to choose a couple more to cross that $199 threshold for an extra 20% discount, come on.... you know you want to