I'm old enough to have seen radiant heat tried for an entire house in the past. It didn't hold up and was near impossible to repair and replace.
I'm sticking with gas forced air heat as my answer :)
So... most resale value in the future for a brand new house today ... most likely isn't gas forced air. I think the popularity is stunted due to it being cumbersome to install.
As far as solar panels...I cannot claim to be overly familiar with them but have seen them around occasionally. It would be a concern here in Seattle with it being more gray so I would really be cautious and talk closely with an expert before moving too far with Solar Panels in this climate.
As to which is best and would be the most valuable when you re-sell, ... my guess is going to be the radiant floor heating. I have planned on putting in radiant floor heating when it's time to get a bigger house cause I think it's really cool and know people who have it really like it. As opposed to a heat pump, ... when I show a house with a heat pump, ..it doesn't garner much interest, unless the client knows what it is.
One last thing, ... of the houses I've seen with radiant floor heating, ..it's been in the whole house.