When you go shopping, how do you determine "that's the ball"?

Personally I first decide the shape hook i'd like.  I then look at core specs, I currently like to look for around 2.48-2.50 RG and .050+ on differential, when i'm looking for the first ball outta the bag.  I like to look for later hook, rather than the early-mid lane grabbers. 

I also like to watch the reaction videos, and see if the ball merely gets to the pocket and knocks em all over, or if the ball gets to the pocket, and throws the pins everywhere with a ferocious vengeance kind of hit.  I don't wanna see marshmallow hits....  On that note, I find it slightly strange, with Storm and Roto being sisters, most of what I see out of Storm right now is either early/mid, or a marshmallow hit, and the Roto stuff hits like a pissed off truck and grabs later.   

Do you like to do surface changes, or are you one that likes oob better?

I just bought a Nail Titanium. I wanted a ball with a pearl coverstock that had length and a good backend reaction. I was also looking for a ball for medium to light oil conditions. There are a number of balls on the market that fit that description. I purchased the ball at my local pro shop where I also relied on input from the pro shop proprietor.

I had done a fair amount of research before I went to the shop---checking ball websites, looking at videos, and talking with other bowlers. So I had narrowed my scope to a couple of balls.

Dave, I like the Nail Titanium so far. It generally has a predictable arc and a good backend reaction. I thought that I might have some trouble on spare shots, but I have done alright with the NT on all spares---except the 10 pin where I use a plastic ball.

The NT also looks great going down the lane---usually not a reason for buying a ball but a plus anyway.

I typically like the ones with bolts and stars on em!