So the question is more that you're thinking of a reason why one is the odd one out and we have to guess which one you're thinking of, because there's nothing wrong with Seraphim's answer - it's a good one.
Springer is the only one with futuristic altmodes is another logical answer. Also, he's the only one who doesn't turn upside down between altmodes. And he's probably the only one with no real scale issues when he transforms from altmode to altmode. But if it's not to do with the altmodes, then I'm going to go with: Blitzwing was the only one released as something else (a Diaclone) before he was a Transformer?
(It's either that or Astrotrain: because he was the only one who was never a 'good guy' in the cartoon.)