It's hard to say what could be better for you between Recalbox and Libreelec + Gamestarter.
It really depends on what you use the most.
If it's watching movies and TVShows, you'd better go with Libreelec + Gamestarter.
Otherwise, go with Recalbox.
I have 2 Pi3 at home, one with Recalbox in an arcade cabinet, and one with Libreelec hooked to the TV.
I can watch Movies and play retrogames on both, but to be honest I believe in your special case Libreelec + Gamestarter might be the best choice.
Recalbox is really useful to play games and build an arcade cabinet as I did, but its kodi implementation is not the best...I would say it's designed for gaming, and the plus is that you can watch movies with it.
On the other side, Libreelec + Gamestarter works like a charm but you need to go through Kodi to access your games.
So as I said above, it really depends on what you do the most but I would recommend you Libreelec + Gamestarter.
Installation is really easy, get the zip, put it on your SD card, then install from Kodi's system menu.
Then launch Gamestarter and configure it (to choose between Retroarch or EmulationStation as frontend).
When it's done, you'll find a new folder called emulators in /storage, and in this folder you'll find some folders including the roms and the bios ones.
In the roms folder, you'll find folders for all the supported systems, just put your roms in these folders and you're good to go.
Really simple to setup.
supported systems are the following :
amiga
atari2600
atarilynx
atarist
gamegear
gb
gba
mame
mastersystem
megadrive
msx
n64
neogeo
nes
pcengine
ports
psp
psx
snes
videopac
zxspectrum