That is not such an easy question to answer.
A "woods knife" means so many different things to such a vast variety of woods folk.
Are we talking about a half mile leisurely stroll to stretch ones legs and maybe smoke a cigar? A three day trek? Survival situation? Hunting? Camping? Wood prep? Food Prep?
Maybe the complication of this proposition lies in all that the woods have to offer and the various ways we all get afield.
Putting aside all of the foregoing, as if that were so easily done, we then get to whether or not we are talking about only having one knife, only one fixed blade or what other implements are at our disposal?
All of that said, I really prefer a blade of about 6 to 7 inches - though I rarely carry such a knife and the BK7, wonderfully versatile and functional blade that it is, is one of my least carried. If I were limited to one knife, the BK2, 7 or 10 would be top choices, but I would typically have with me afield a multi-tool, a SAK and, at the very least, a stout folder such as a Sebenza 25 or a BM Adamas.
On to fixed blades, a Mora (I like the Companion HD in carbon steel) is light weight and darned near a
must have in the woods; therefore, it almost doesn't even count - you just should have one with you. I am a fan of having on my belt a Tweener (BK15, 16 or 17)
AND a larger fixed blade such as a BK4, 5 or 9. For wood processing and heavier work, the BK 4 and 9 are legendary performers but when it comes to the slicing and dicing of camp food prep, my beloved BK5 is best - oh, and it lops and does other wood prep better than it's slicing ability would have you believe. Oh, forgot to mention that a BK11, 14 or 24 should be on your neck - just because.
Notice that in none of this is a BK2, 7 or 10 - versatile and useful though they may be. In fact, a 6 or 7 inch "woods knife' is dandy for many outings with the BK2, 7 or 10 being among my very top choices in that regard.
Did this large circle that I drug any hapless reader on make any sense given that we wound up not too far from where we didn't start?