I've seen both as well, but predominantly it's like this:
Largest cusp on maxillary molars: mesiolingual
Largest cusp on mandibular molars: mesiobuccal
Think working cusp. If you're chomping on it, you want it to be big.
Watch that it is looking for size and not length/height or width. I know you're talking size here, but when reading other questions you'll see some that want height or width. Here are some random samples from different sources on the matter.
2012 - 2013 Decks:
Mandibular first molars: The mesiobuccal cusp is the largest of the five and the distal cusp is the smallest. Lingual cusps are higher and more pointed than the buccal cusps.
Mandibular First molars: There are five cusps. Of them, the mesiobuccal cusp is the largest, the distal cusp is the smallest.
Mandibular First molars: The mesiobuccal cusp is always the largest and longest cusp, occupying nearly two-thirds of the buccal surface.
First Aid Q&A:
Mandibular First molars: The mesiobuccal cusp is always the largest and longest cusp, occupying nearly two-thirds of the buccal surface. (same exact wording from decks)
First Aid:
Mandibular Permanent First Molar occlusal morphology: MB (largest), DB, distal (smallest), ML, DL
Mandibular Permanent Second Molar occlusal morphology: Has four cusps: MB, DB, ML, DL.
Mandibular Third Molar occlusal morphology: Has four of five cusps: MB, DB, distal (can be absent), ML, DL. MB cusp is larger than DB cusp.
Woelfels Dental Anatomy is one of the NBDE reference texts (ADA Recommendations):
Mandibular 1st heights (longest to shortest): ML > DL > MB > DB > D
Mandibular 2nd heights (longest to shortest): ML > DL > MB > DB > D
1996 Released Question:
Which of the following represents the largest cusp of the mandibular first molar?
Mesiobuccal
