Assuming you meant Z77 vs Z68 then there's a three advantages with Z77: 1. Native USB 3.0 support, 2. Lucid Virtu MVP which allows better 'improved' options with iGPU & Discrete GPU(s), 3. PCI 3.0 though there were some Z68 with 'GEN3' chipsets (PCI 3.0). (4) Few will benefit from the 3 monitor potential of Z77's.
Nice summary - http://www.pugetsystems.com/blog/2012/04/12/z68-z77-and-h77-whats-the-difference/
Potential problem -- Most and not all Z68 MOBO's support an IB (Ivy Bridge) CPU and those that do require BIOS upgrade OR they will not post. The fix is to borrow a SB CPU and update the BIOS or have it sent out for repair or minimally shipping costs to OEM.