Naturally when you're looking to buy a game, you want to get the latest and greatest version. It should have all the extra content, bug-fixes, and so on. However, the possibility exists that the newest verson could be inferior in some ways. Game-design is a constant and always finicky, and nobody ever seems to be satisfied with its results. So things get changed, and changed again, sometimes they're even changed back to their original state. It's a constantly confusing nightmare, and for what? In the end it all comes down to preference.
Forgive me, I love to ramble.
STCE is on paper*, the superior version of Guacamelee! Let's look at some of the facts:
Two brand-new areas to explore!
A new boss-fight!
Every foe has a visible health-meter!
If you're hankering for more Guacamelee, then definitely grab this! The new areas are great. They make the world a bit richer, and are fleshed out with plenty of secrets and fighting/platforming to be had. I also like the little changes such as costumes being unlocked via silver coins. The biggest deal is that the controller-issue I had with Guaca-Gold is fixed, making this by default the superior version for me.
STCE is a different game, and it can be considered inferior in a way. The controversial addition is Intenso! It's the "shock gloves"** of Guacamelee. Once you fill a meter you can become a superpowered luchadore by pressing L3+R3. Once you purchase all of the upgrades you're practically invincible. Guaca-Gold wasn't a difficult game, so having the ability to cheese the rare moments of challenge makes things a bit too easy. Keep in mind that this ability is optional. Most of the time I forgot I even had it.
The new enemies are quaint. For the most part they're reskins that can move faster, hit (much) harder, and will sometimes teleport to get out of danger. Aside from nega-chupacabras doing tons of damage with their sword-stab, they're not a threat. There are also some flying fish in one of the new areas. They remind me of enemies from the Saturn version of Symphony of the Night. They only showed up in one area, and behaved in a similar manner. If it's a reference, then I applaud drinkbox for their attention to obscurity.
If you haven't played Guacamelee before, IMO it's best to go straight to this version. It's more convenient, since the original version doesn't have multiple save-slots. Having the most content is a definite plus as well. You might feel the urge to go back to Guaca-Gold for its original "true" level of difficulty but eh...I wouldn't recommend it. Most of Guacamelee's challenge is in a couple of boss-fights, and the optional areas like El Infierno. For the most part you're the awesome skull-cracking luchadore on a fun adventure. If you want a difficult Metroidvania, consider Valdis Story: Abyssal City (also on Steam).
Mostly though I'm just really happy and relieved that the controller issue I had with Guaca-Gold is fixed in this game. It's the main reason I'll probably never go back to the earlier version (though I have a fair number of achievements I should get).
*What is it with "on paper"? I use that phrase way too often.
**The gloves from Batman: Arkham Origins. Punch through any defense, combo count boost, makes things so easy.