It really varies by world, it all depends on what coaches are occupying the posts around any given position.
Of the Power conferences, the SEC is pretty good for “under the radar” status, in that there is only one A+ team (UK, on the northern border of the conference), so there’s a lot of parity, and as a conference can kind of dominate the gulf coast up into the southern Carolinas and Tennessee-Arkansas. But if it’s full of good coaches, it can be hard to stand out, as you’re all packed in pretty tight.
I cringe at the thought of Rutgers being mentioned here. Obviously it’s possible given the right circumstances, but in my experience, Syracuse and UConn have eaten their entire lunch in conference, and then you constantly have the power of the ACC coming up on your south as well. And with the A10 becoming en Vogue as a powerful mid major, Rutgers is rightfully one of the first posts abandoned (from what I’ve been seeing). But as always, it depends on the world and the coaches. The right coach in the right situation can absolutely make it work.
Those mountain west schools are usually good, if the conference isn’t too crowded. Air Force, Utah, etc.
I’ve long been convinced that Fresno State is a better job than it gets credit for, and while I have to deal with the GOAT in Piman at UCLA, I’m making some progress now in the first half-dozen seasons, and should have them established as a perennial S16 *caliber* team in the next couple seasons. Recruiting in Southern California while playing in the Pac10 north is helpful, only playing the powerhouses (UCLA and Zona) once per season.
I also really liked the Big Sky, and overall, I think geographically that has the most potential for the kind of “under the radar” teams you mean, if you get the right coaches in the right spots. Get 8 coaches in there, so the conference RPI gets up in the top 10, and you can get 3 teams in the NT pretty easy I think, more with the right coaches. And since it’s so spread out geographically, everyone can kind of naturally do their own thing, fight their own battles.