One of each (and a 29er! 😉 ) is the answer… It's the only way!
In all seriousness though, I rode full sus bikes almost exclusively for years. I grew up riding rigid (because I couldn't afford decent sus forks at the time) before progressing to front sus, then quickly to full sus as I thought it was the holy grail.
In the last 14 years, I've owned all manner of different full suspension bikes, and a few hardtails, and I can honestly say that there have only been a couple of hardtails I've actually liked in that time. Several of them, whether it was the geometry that was off, or they were too stiff or whatever, I didn't gel with them. That said I love both the hardails I have now (Genesis Altitude 853 and a 29er On One Inbred), and am hoping the recent addition (Cotic BFe frame) will prove its worth too.
I think the biggest problem was that I had some very good full sus bikes over the years, and I'd become a bit lazy on them cos they let me get away with a lot. To jump onto a hardtail that didn't feel that right in the first place, meant they often got sold pretty quickly. But I just gelled with both my Genesis and my Inbred straight away, and as a result they get ridden loads more than my full susser these days!