Without knowing the specific lane conditions, you're bowling on, there are a few general suggestions I can think of right off the top.  For medium, definitely the Sigma Sting.  It's a pearl that's clean through the front, reads the mids well, and is a bit angular on the back.  Think more hard arc.  The great thing about this ball is that in the short time I've had it is the versatility.  It's a true benchmark piece that will allow you to play straighter as you want, or hook the entire lane like EJ Tackett did with both of his Sigma Stings during the Japan Cup.

Medium-Heavy, I'd go with either the Covert Revolt if you want something smooth in reaction or the Primal Rage if you want skid/flip.

For lighter conditions, there always is the Venom Strike (solid), Venom Toxin (hybrid), and then the Tribal (pearl).  The Toxin can most likely be bought for a good deal as it will probably be replaced by the upcoming Tribal Fire.

I think I am going to try the Primal Rage
house is mediume-heavy 
do you think i will be able to go down and in with it?

Haven't posted in awhile but needed to give a shout out and a thanks to Tommyboy74.

I have been reading his posts on the Sigma Sting and being a strong Storm/Roto guy like he is, was reluctant to try something else as these 2 brands have really worked for my style( after years of trial and error with other brands)

Well I'm glad I listened as I feel the Sting maybe the best all around medium league THS condition ball I have ever thrown. Until I thru this ball, that statement was reserved for my 2 victory road solids with different drilling/surfaces.

The Sigma Sting has now taken the spot of those 2. What an outstanding ball! You know what's it's going to do shot after shot. Hits really hard with great predictability.

Thanks again TommyBoy74 for your posts on the Sigma Sting! It was the first, but won't be my last Motiv ball.

Gonz

Well, bowlers on the pro tour that have thrown the Primal Rage say the continuation on the backend is very impressive.