GA-Z77X-UD3H vs. GA-Z77-D3H

No, its not worth for $40 more. Actually both are not worth for you. As you want to use a i5-3570, which is a non-k edition, no need to get a z77 chip mobo. H77 is enough for you and you can save some money.Look for this one:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

It only cost $70 and has everything for you. Gigabyte h77 cost $95. Thats why i suggest Asrock for saving money.

So if i were to use an i5 3570k, which motherboard would be best?

As I look, the lowest price you can get UD3H is $139, and D3H is $129. For $10 the UD3H offers better connectivity, (more SATA 3 ports, more flexible RAID options, and an extra PCIe 3.0 slot*) support for faster memory - up to 2666 Mhz and a couple more USB ports. That plus the overclockers'/enthusiast features like a dual bios switch and onboard power and reset buttons would be worth it TO ME. YMMV

* - It's not really an 'extra' slot. Both boards have 16X, 8X and 4X PCIe slots. The difference is that they are 3.0, 3.0 2.0 on the UD3h and 3.0, 2.0, 2.0 on the D3h.

Best answer selected by tomminater.

who says that 3570 non k cant b oc. ive done it to 4.3 ghz with ga.z77.d3h mb using easy tune.

You oc by increasing BCLK. K-edition have built-in oc feature.

you really need to compare the z77x d3h with the z77x ud3h and not the z77 d3h