Your friend is similar to myself where I came back after a layoff too. Glad to see him back. Here some ideas that could work as it seems your friend has a similar game to me.
From Storm, the Virtual Gravity Nano is absolutely a great ball on heavy oil. It's strong but layouts can help tame the backend. Absolutely a great ball for heavy volume. Also, I could recommend a Storm Anarchy pearl for medium-heavy and the Storm Virtual Road is a great pearl ball that works well with medium conditions.
In addition, Roto Grip (sister company to Storm) makes a lot of great equipment that is priced well. For medium conditions, the Nomad Dagger hybrid is a nice choice, giving the benefits of pearl and solid with preventing some of the overreaction. Also, the Rising Star hybrid is a great ball for medium-dry conditions. Again, the hybrid helps blend out the conditions and gives a predictable reaction.
Even though I use Storm/Roto Grip in my arsenal, 900 Global/AMF also has some great equipment out there. I would recommend the Bank or OMG! solid (heavy), Bank Pearl or Shred-It hybrid (medium-heavy), the Favorite (solid), Long Shot (pearl) or Double Clutch (solid) for medium oil, and then the new Hook (solid or pearl) or Smoke (pearl) for lighter conditions.
Now these are just suggestions, but those would give a good start. I'm sure others will chime in with other suggestions from Track/Ebonite/Columbia/Hammer, Brunswick and the other brands. The good thing is that all of the brands produce great equipment to work with today. My advice would be to stop in a bowling alley during league night if possible to see what some others are throwing. In addition, some pro shops now have test balls with interchangeable grips that allow people to throw them before buying. If your friend has that nearby, that is definitely a must. Finally, the manufacturers have demo days and those are also a great chance to throw before buying.
My arsenal
Heavy Oil: Storm Virtual Gravity Nano: 4000 AB
Medium-Heavy Oil: Storm Anarchy: 1500 polished
Medium Oil: Roto Grip Nomad Dagger: 1500 polished
Medium-Light Oil: Roto Grip Rising Star: 1500 polished