MyCredits and MyStore are doing it great, but if this project doesn't go on, you'll be passed by MyPlaza Turbo (1.4 version of the original MyPlaza).
Both MyCredits and MyPlaza have great ideas and great stuff, but MyPlaza is more featured and it has a lot of great stuff.
Have a look at here: http://forums.consoleworld.net/plaza.php (you must register)

MyInventory is my favorite, since I'm starting a new RPG project, so that users can buy stuff for their battles and all that (swords, shields, orbs, and all those rpg stuff).

I love MyCredits and MyStore, but if someone doesn't work with MyCredits really hard to beat MyPlaza, I'm sorry.. but I'll have to move to MyPlaza. It just looks great.

Greetings,
Icy

They are really two different systems. I personally think MyPlaza is overly complex. But that's just me. If you want to move to MyPlaza, it's very easy to. I'm more busy than Pirata(or whatever his name is), so it's up to you about which one is better for your site.

Well I'm using it right now and it is complicated to say the least. I could use a lot of work honestly ;).

It all comes down to your personal preference. Both plugins were quite well, in my opinion. MyCredits is a very simple, easy to use points plugin, for those not interested in a store to accompany it. MyStore was made for those who like to keep things simple, while being able to add a nice little store plugin alongside.

MyPlaza Turbo is much more complex, and advanced, so some novice users may not feel as comfortable using it, while expert users will most likely use it over Mystore. So at the end of the day, it's all down to your personal choice.