You raise a good point, especially as "best" is so subjective. You've really made me think about this.The trick is to avoid "paint by varietals (numbers) e.g. Cabernet Sauvignon + Merlot + Cabernet Franc has to the best. No it doesn't.
The more I think about it, I don't believe the label "best" can be applied to any wine. "Best right now"? Sure, as "best" requires a qualifier. In my thinking, I don't even consider "best" -- I choose varietals that will produce a good outcome.
This fall I'm planning a pair of 3 grape blends (Cabernet Sauvignon, Cabernet Franc, Merlot) with CS dominant in one and CF dominant in the other. Why? Because a commercial wine I've loved for decades is a CF dominant blend with CS and Merlot, so why live with a few bottles if I can make a few cases. And since I'll have a bunch of CS, I might as well make the other blend as well. My experience with red Vinifera is that these blends will turn out good -- hopefully very good.
The word "experience" is key, as I'm working off my own direct experience as well as the experience of others. The Red Blend Ideas thread I started a couple of years ago is geared towards this -- folks post the blends they've made that worked out well, to give others ideas that should work out well.
My takeaway from your comment is to always think things through and make an informed decision.