Re: I never use the middle position on my Strat. What to put there?
Like you Diego, I never used the middle pickup alone very much, though I spend a lot of time in position #2 (bridge + middle). Two things have changed that.
First of all, I sold my 1960 Strat in 1990 after a divorce. A couple of years later I went looking for a new Strat, but wound up buying a new G&L Legacy. I've become a huge fan of G&L--after all, G&L was Leo Fender's last guitar company, and he came up with some great improvemnets over his original designs. One of them is his Pasive Treble and Bass control system. It allows you to have control over the bass and treble (not just a treble roll-off); and it it global, meaning it works on all pickups in every switch position. It's a really good system for dialing in the middle pickup--I still don't use the middle alone a lot, but I certainly have been using it more and I've been much happier with the tones I get from that pickup. BTW, the PTB seems to work even better on the G&L guitars that have hotter pickups--like the Comanche, S-500 and the Legacy Special.
I like the vintage Strat tones of the stock Legacys, so I don't do a lot of pickup swapping in these guitar. I bought one used Legacy a few years ago, and it came to me with Duncan Texas Hot Antiquitys. I doctored it up a little more, and replaced the standard TH middle with a RW/RP middle, and then replaced the bridge with the hotter Custom Bridge Antiquity. The warmer tones of the Antiquitys in this ash-bodied Legacy are really something special. Don't get me wrong, I still love the snap and quack of my Legacys with stock pickups, but this one definitely has a different flavor. I do find myself using the middle pickup alone more on this guitar. Normally, I'd use either the bridge or the neck or position #2 for my solos, but the middle pickup alone in this guitar works great for solos. If the bridge is a little too edgy or bright; if the neck is a little too sweet or dark--the Antiquity middle seems just perfect. Without a doubt, the best middle pickup tone I've ever gotten from a Strat-bodied guitar.
I'd never give up the middle pickup on a Strat, because I love the position #2 quack so much. Unfortunately, I can't really make a pickup recommendation to you, only what works for me, but I hope this helps.
Good luck in your quest.
Bill