Which one is better?? If this has been posted before i didnt see it
As of now, Simba is pretty much the same as Scar.
Scar was the big one from 2004~5 ish to 2008~9, when Simba was introduced, more people was switching over to Simba from scar. Since then scar scripts did "die down" for a bit as freddy was busy working on it; Thus every one else continued using simba and making scar scripts rarer and rarer.
If some one wants to use a simba script on scar, they could do it within 10 minute. Both of them still has 99% of the same syntax and every thing should be compatible with SRL (Which is the library that the entire villavu.com community is working for).
Right now, Scar is moving towards botting in general (for other games as well as runescape), and may not have Support SRL; Instead it will be using its own OSI (Offical Scar Include) as well as partial C++ support and multi threading (?).
Simba will continue supporting SRL (Scar Resource Library) but it is currently waiting for SRL 5 to be released (which won't be Scar compatible).
Summary:
Right now, Scar = Simba. In the future , Scar != Simba.
The are almost the same. But with scar currently building on more scripts right now and developing new version (scar titan) where simba is working hard towards SRL 5.

