In middle position, the notation of "call 1/2/3" starts to expose more differences than it did in EP. I'm going to do the chart from the perspective of assuming you have enough callers to meet Matthew's criteria and then add some notes at the end about that.
In an attempt to head off a frequent criticism, I agree that most people overuse pre-flop charts and that you need to be making your own independant decisions. I'm fully down with that point of view. I mostly started to pursue this line of thinking because I find these comparisons interesting to myself and because I frequently see complaints that Miller is too loose pre-flop and I wanted to see if that is objectively true.
The differences:
1) K9s/Q9s -- Miller says to limp, Hilger says to fold. The advanced section of ITH doesn't discuss these hands. I tend to play K9s/K8s and other Kxs when I think the table will not likely raise behind me and/or there are likely to be many to see the flop. I always fold Q9s.
2) KJ -- Miller says to limp, Hilger says to fold. I used to fold these hands and I've started limping since I read SSH. I'm finding it a slightly -ev play for me thus far.
3) 99 -- Miller says to raise, Hilger says to call. I almost always raise. ITH does say you can raise this hand in the advanced section either first-in or against one limper. I like to raise this hand to try to discourage Ax type of hands.
4) KQs/KJs/KQ -- Miller says to raise, Hilger says to call. I always raise first-in with these hands and frequently raise against callers. In the advanced section, Hilger would have you raise these hands first-in or against one caller. The advanced section also looks at raising 88/77/A9s/A8s/A7s/KTs/QJs/QTs/JTs. I wouldn't raise the Axs suited hands, but I often raise the others first-in.
5) TT -- Miller says to re-raise against a raise, Hilger says to fold. I follow SSH's advice against all but tight raisers with good results. ITH essentially provides the re-raise advice in the advanced section, so this isn't much of a difference
6) JJ -- Miller says to re-raise, Hilger says to call. Again, I almost always re-raise and the advanced section essentially concurs.
7) AQ -- Miller folds to a raise, Hilger says to call. I actually usually choose the third option, re-raise. The advanced section would allow the re-raise.
8] KQs -- Miller says to call a raised pot, Hilger says to fold. I'm with SSH on this one. I like how KQs plays heads-up or multi-way.
9) 66/55/44/33/22/JTs/J9s/T9s/98s -- Hilger will only call these with two or three people already in the pot, Miller will always call. I mention this because having three limpers ahead of you from MP isn't always very easy -- so you will fold these hands more if you follow ITH. Of course, I think fudging the "call 3" when you expect that there will be several limpers behind you and you don't expect a raise is probably the first place where most people venture away from the ITH chart, but I thought it was worth a mention.
My conclusion is that we are still looking at pretty similar advice in MP. Unlike EP, where I think ITH is actually a bit looser, I'm going to have to give the looser nod to SSH in MP, although it is still very close. If you factor in the advanced section, K9s/Q9s/KJ in an unraised pot and KQs in a raised pot are the main differences where SSH will play them and ITH will not. The only argument for ITH being looser is that he might raise 88/77/A9s/A8s/A7s/KTs/QJs/QTs/JTs first-in if the conditions were right. When you add back in that ITH would sometimes fold 66/55/44/33/22/JTs/J9s/T9s/98s unless there were several callers, I'm awarding the loose points to SSH by a very small margin. I think you still have to reject the argument that SSH is dangerously loose pre-flop.

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