At least for me, I find most of the above to be somewhat useless: The first three because I book straight into First, and the day passes because I'm on the wrong side of the country.
With that being said, the Gold 100% point bonus is quite juicy and worth aiming for in my mind, in no small part because in the long run it turns the program into more or less a straight 20% discount on flights, coupons or not. The fact that points basically convert straight into dollars is nice as well...so I guess what I would nominate, in lieu of "No blackout dates/restrictions", is the extreme simplicity/straightforwardness of the program even beyond that. That may not seem like it's saying much, but when I look at a lot of other programs my eyes glaze over rather quickly with all of the charts (alongside blackouts and restrictions).
My second choice, for what it's worth, would be the partner offerings with the other Virgin airlines plus Singapore and Emirates. Being able to redeem points on partner airlines that have a sense of class, if you will, does stand out. However, I also know a lot of airlines have other deals on offer, so that doesn't stand out as much.