My last AR had a 1:12 barrel, but i notice a lot have 1:7 rate and others have 1:9

ok, now for the dumb part of the question.... which is better?

None of them are better, just different. A faster twist like 1x7" stabilizes long heavy bullets, but creates so many RPMs that lightweight bullets (below 55grs) may have their jackets torn off, resulting in no downrange impact. You have to drop velocity severely to allow light bullets to function properly in a fast twist. A slower twist such as 1x12" will not stabilize bullets much over 60grs. The bullets will wobble and keyhole into the target downrange.
Best compromise IMHO is a 1x9". For highpower, 1x7" is probably better. I don't really see any reason for a 1x12" as it gives nothing that the 1x9" twist doesn't.

Depends on what you are wanting to shoot ammo wise. 55gr will be fine in 1:9 heavier bullets will do better in a faster twist ie. 1:8 or 1:7.  1:9 is generally good up to ~65gr if you want to shoot matches with specially prepared match ammo you will probably be better served with a 1:8. If you just want a fun shooter that will shoot cheap mil surplus ammo go with a 1:9.

...so it's not good to shoot 55g bullets in a 1:7 ?

The industry standard seems to be the 1X9, simply because it is a versatile twist.  Others, like Glen Zedeker (sp?) advocate the demise of the 1X9.

Sure, 55grn fodder will "work" in a 1X7.  I believe that the government went from 1X12 in the M16A1 to 1X7 in the M16A2 to accomodate a shift from 55grn ammo to 62grn ammo.  The story goes that 1X7 is a bit "fast" for the issue tracer rounds which caused premature barrel wear, so the 1X9 came into the forefront.

If you're using your AR as an all around rifle, then your barrel twists will suffice.  If you want to start shooting serious competition, then you might want to think about a free-floated Krieger 1X7.75 or a 1X8.

But don't sink any money on new gear until you learn to read the wind, work the pits, shoot from position, etc.

I think what you have is fine.  When you need to replace your barrel due to throat erosion, then get something new that meets your specific needs.  Don't let anyone talk you into something just for the sake of getting something new.

Unless you want us to, and then we'll tell your wife that it was our fault!

Quoted: ...so it's not good to shoot 55g bullets in a 1:7 ?

55grn bullets were designed for 1:12 twist barrels and - as a general statement - will be more accurate with those barrels.

In a 1:9 twist barrel probably around 62-64 grn is optimal.  (Probably the 1:9 barrel is the most versatile.)

"TROY" - one of the mods has an excellent paper on bullet weights vs. barrel twists.  Also there's a member named "forest" that's well versed.