Thank you for porting the MAME core to libretro / RetroArch, it feels so much better than using the official MAME builds or MAMEUI / IVPlay.
Yet, why was version 0.78 ported instead of the latest one, 0.149u1? It’s just that there are some games that I wanted to play that aren’t supported by either FBA or version 0.78.
078 was chosen because it’s very fast and covers many of the classic arcade games not covered by FBA. There’s a new port being worked on for newer, faster devices, based on mame v0.139 that will be able to cover many more games, obviously, at the cost of some performance.
Yes 0.78 is less compatible but recommended for performance on lower devices. 0.139 is more compatible but more slower .
for example on RigdeRacer with mame2010-libretro ( with no frameskip and X86 DRC enabled ) :
on a laptop with Core 2 Duo CPU T7700 @ 2.40GHz , i only have between 60% 70% of speed.
on a laptop with [email protected] and i have 60fps and fullspeed in game.
on a htc desire S ( old MSM8255 1Ghz) i have 10% of speed 
And 0.149 is even more slower , with an unreleased mame0149-libretro (with no frameskip and X86 DRC enabled ):
on a laptop with Core 2 Duo CPU T7700 @ 2.40GHz , i only have between 35% 42% of speed. on a laptop with [email protected] i only have between 87% 92% of speed.
on the other side 0.149 is more compatible ex: tekken3 works great on it , but segfault in 0.139.
Now i really want to know how does 0.139 or higher can works on a GalaxyS4 or a NV Shield.
Thank you for the replies. =)
So it all comes down to performance. While it does make sense, surely we could have two MAME cores no? One aimed for low-end devices (that would be 078) and another one for high-end devices (the latest MAME version) the same way there are two SNES cores for RetroArch (bsnes and snes9x).
Still, it’s already great to know that there is a more updated version of the MAME core being ported to libretro.
Actually from what I understand three versions are gonna be mantained, 0.78, 0.139 and mainline