Hmm... I guess I'd go Lehr, Windhund, and 101st Airborne if I don't know the map and opponent. There's some divisions that I think are a bit weaker than the others, and several Allied divisions have gaps in their anti-armor capability that makes them particularly sad on certain map/opponent pairings, but in general there's really few that make me say "oh, that's terrible in 1v1!"
So, my top 3 in descending order of difficulty:
I think the Lehr are tricky. You get very little infantry until Phase C and no tanks until phase B. You need to be really good at making up ground, although as a consolation prize your Allied opponent will be pulling his hair out at his inability to stop you from pushing through open ground once the big cats arrive.
The Windhunds are in the same boat when it comes to opening with almost no infantry but ultimately getting big cats. However, they can open with a strong Panzer III rush in A and then start getting reasonable quantities of infantry in B, so they're handicapped for less time. In exchange, however, you don't get the big cats until phase C and have bad phase B tank options so you need to have a good phase A and don't have a lot of time to exploit your armor advantage when the big cats arrive.
The 101st Airborne are actually extremely good on the right terrain, but in general they're a deck that is weak outside of a narrow niche. If you end up on an unfavorable map or against an opponent who is good at exploiting that, you may have a challenge on your hands.