Can't speak for FP or CT but Purple Hammer is my favorite urethane ball of the dozen new and old school ones I own.  Best carry have seen with urethane and is very strong but not super early like most urethane.  Highly recommend.  Purple Hammer have far outsold the other two from what I understand as well.

I have one Fever Pitch and two Covert Tanks (drilled very different w/ different surface).

My 5 in Pin to Pap Fever Pitch is close enough to the 4 1/2 Pin to Pap Covert tank, that, really no need for both. I almost only use non-reactive and so was curious and excited to get Covert Tank, although I didn't have a big need for it. 

Then the 1 in Pin to Pap with 4000 polished surface Covert tank is to go between those two and my weak urethane ball.

For  most layouts the balls are so close, can just go with whatever company you like. Fever Pitch is slightly more skid-flip. If I had to choose just one, I'd go with Fever Pitch, but it's close.

The advantage to the Covert Tank is the larger differential, so can do more with different layouts.

I hate carry down and the way to avoid that with these balls is to get the track to flare. Fever Pitch flares enough so oil rings separate, but would not with a 1 inch pin to PAP.

Covert tank flares a lot. Even on 1 in pin to pap I get some separation. So I would go with that if want to put on a control layout.

I did not get a purple hammer because it has a .013 differential at 14 lbs. So unless you are in a tournaments and moving every games, you will very soon be playing in your own carry down. Although the 16 pounds is 0.30, so that will flair.

I really don't care how many people rave about Purple hammer, I had zero interest in a urethane ball that can not flare. and with a .013 diff at 14 lbs, and .015 at 15 pounds, it's not going to flare no matter what layout it used.

As a rev dominant player, with about 3 degrees of axis tilt, who bowls on sport conditions, theses balls are amazing. I've seen enough people complain about Fever Pitch. It's my favorite ball ever.

These balls are not bad when used for the purpose in which they were made. Control on difficult patterns. Great for high rev players on sport conditions. As a no thumb bowler with low axis tilt I feel like these balls where made for me, and maybe with all the two handers now, they were designed for players like me.

On a house shot, I'm better of standing left and chucking a reactive ball right.

Both these balls have much more pop on back end than traditional urethane and you avoid the carry down issues. Compared to my blue hammer, or Natural Pearl, I have to move about a whole arrow left.

Everyone is playing catch up to the Purple Hammer. They are trying to figure out the formula, and right now the Purple is King. It is a top 5 seller of all balls made for a few months now.

I had all three hated the Covert, didn't like how it rolled all balls drilled the same. Fever Pitch was better but it was hit or miss. Purple is the only one of the three that I know what it will do, very consistent..

16.5-18 mph off my hand (monitor), 540 rpm, about 55 rotation, 3-4 degree tilt. My personal opinion, the 16 lb Purple is the best urethane on the market. I had a 15 lb, drilled it stronger to try to conpensate for the lower diff, didn't care for it. Unless you're rev dominant or literally point the ball, I wouldn't touch a 14-15 lb Purple. The Fever is honestly really good. Not as good as a 16 lb Purple, but it rolls pretty darn good. It's cleaner and flippier off the spot. Fever is also very good shiny (whether it's lane shine or polish), but it won't offer the control you need for fresh harder sport. I can't speak on the Covert since I have no experience with it.

I guess I’m in the minority, but the Fever Pitch has been that go to piece for me, when I need control, and stronger, but predictable motion on the short patterns, and lighter conditions.  To each their own I guess.

It's all good, thankful for multiple companies...

It looks like a new Tank has been approved on the USBC site.

Wonder if it will be a limited edition like the Combat Tank.

If it's a pearl version of Covert Tank, that's another toy to buy.