Okay... Let's admit, We're likely gonna see a lot of Ponymaker ponies.
[It's not Always a bad thing! Iccy came from one!]
Hasbro, Catching on, Released an official Ponymaker, Not TOO different from the one on the Market.
Hasbro's Official Ponymaker
And the Fanmade one that's out there.
There's quite a few differences, however... Let's look at the official one first, Since We've seen the unofficial one at least once.
The official one
Once you learn the trick on HOW to use it, [Took me a while to figure out that, yes, You use ARROW keys.] It's actually pretty easy to use. Each is broken up into options, [As compared to the fanmade one, which gives you Sliders] and There's numerous combinations.
There's also less color choices, and more Guesstimating. Unlike the slider format of the fanmade one, the official one gives you a set box of tones. It took me a while to find Grey, for STEAM!Iccy.
Another thing, You can't import your own cutie mark, which is both a blessing and a curse. You either A) Draw your own, B) try to photoshop it on or C) Choose from their selection.
I should note, also, There's choices for Ticky, Indigo, and Night, but not Iccy. Sadly. (Not even Arch-Rival's Cutiemark!)
There's TONS more clothes than the fan version brings, including vests, Neckwear, hats, sleeves, fore-legs, rear-legs, And capes, [which also includes skirts!] All the color choices are chosen from the same menu, [Which makes it hard to blend,] but works out anyway.
The hairstyles are mostly different, [Sadly, I had to make a change on STEAM!Iccy's hair,] And the Tails are slightly different too.
Oh! And There's Steampunk clothing in the official one.
So... Here's Iccy for Comparison.
STEAM-Iccy, made with the official one.
Normal Iccy, Made with the Fan-Game.