Strange was being humble...he has the better feats of the two of them (even if Strange sometimes lacks a bit in sheer output of force). Properly prepped, Strange could probably do it. Sentry (maybe), Mr. Majestic has a decent shot.
Really, though, there's probably no one. Thanos bridges the gap between Skyfather and everyone else. He's in his own class, and it's hard to find a suitable (single) opponent for him that's not above Skyfather.
Warlock is the only being who can wield the soul gem properly. The soul gem has vampiristic tendencies. It sucks the juice out of anyone who uses it. Warlock has an affinity to all the gems, not just the soul gem.
Like this:
Thanos with the IG = Kid with a Machine Gun
Warlock with the IG = Navy Seal with a Machine Gun
Strange. I'd even say (As taboo as it is), Strange's raw power equals that of Thanos. Yada Yada, fanboy fanboy. But, Strange is his clear superior in versatality.
Strange even said only one who has a chance is SS
Yeah, I have that. It goes against Strange's previous battles. It makes no sense.
Strange has not only blasted THROUGH a basically fully fed Galactus, putting him out, he's mentally owned him.
Compare Strange feats against Thanos' feats when they fought Galactus. Strange's shield took the same blast that Thano's shields failed to take.
If you were to allow Strange 2 minutes preptime, with no CIS PIS, he would handle Thanos. Strange could just throw a friggin purple gem at him. It's basically a soul gem, but can only used as offense.