Holla really isn't good at tackling, and would like to see some footage of some hard examples, as there are precisely zero of them lodged in my memory. He's also painfully slow, and doesn't impose himself on the game enough. Stephens, by contrast, is a hard tackler, has physical presence, is far more dynamic and energetic, has a range of passing as good as Holla's (there were a couple of brilliant long passes against Blackburn) and, also, gets into good positions, from which he sometimes scores.
I thought Holla started last season really well, then ever so slowly disappeared.