I have some Daiwa baitcast reels that have both of these magnetic braking systems.  

What's the difference, is one better than the other?

I think current Daiwa baitcasters have the Mag-force Z, like the Zillion.

What's the difference, is one better than the other?

They are both meant for different apps.

The Mag Z reels excel at pure casting, they also perform better with a bit heavier weights.

Mag V reels excel at pitching and close range casting with lighter weights.

Is that set in stone? No. I use my Sol (Mag V) for pure casting on an EC68MXF and it does well.

Magforce-V is for V spools, Magforce-Z is for U spools. By design, the Z brake is a little better. It all depends on if want the smaller framed reel that comes with the more compact V spool, or if you want the larger reels that have the U spool. In "theory", they are the same braking system, but the Z works a little better.

Smaller framed reels are the Pixy, Alphas 103 and type F, Sol, ect...

Larger framed reels are the Fuego, Zillion, Steez, Alphas 150, ect....

Magforce-V is for V spools, Magforce-Z is for U spools.

True

By design, the Z brake is a little better.

True, it controls better the tendency of the spool to over run when casting heavier baits

It all depends on if want the smaller framed reel that comes with the more compact V spool

Not true, the Fuego and Zillion share the same frame with the TDZ but not the same spool; the TDZ has a Mag V because it has a V spool, the TDZ BBS has simple Magforce ( U spool ); the Steez depending upon the model, which both have the same everything except for the spool, will have Mag V for the 103 ( V spool ) or Mag Z for the 100 ( U spool )

The situation here is, a reel with Mag V casts very well and less effort lighter baits ( < 3/8 oz ) but when you increase the weight the spool begins to show signs of over run, a reel with Mag Z casts very well heavier weights because it controls more the spool over run but a reel with Mag Z doesn 't cast as well lighter baits.

A reel with Mag V is touchy when it comes to controlling the spool rotation with heavier weights, you tie a heavier weight than 3/8 oz you have to increase the break setting otherwise the spool spins ouyt of control.

Yeah, I guess the frame size is not set in stone, is it???? I didn't even look closely at the new Steez to see the major change on it was the smaller V spool.