You have to look at the booking/fare class, a single letter like Q, T, H, B, etc.

I agree that Delta and Alaska are what you should consider. Roughly speaking, Flying Blue is better only if you regularly fly in higher fare classes and travel to Europe. Delta has a quite good value for miles, it is just that there is not much availability for award flights. But as far as Flying Blue is concerned, if you fly in the US, the situation is not better. Also with a US-based program it is much easier to get more miles by using credit cards.

To decide whether it should be Delta or Alaska, just look up the amount of miles you would typically get for your 5 annual flights and compare what you would receive for it in terms of award flights. So you have to do the Math.