One advantage of Lakka is that it will get core updates first, since it's the official frontend of RetroArch. The setup is complex, but, considering most every other retro gaming OS uses RetroArch as well, if you want to fine tune your experience you'll have to dwelve deeper into it.
Another advantage of Lakka: it has its own frontend which is actively updated along with RetroArch. RetroPie and Recalbox use EmulationStation, which looks very pretty but is no longer maintained by its creator and has a few critical bugs (like the white screen one).
Disadvantages of Lakka: there may be less handholding since it's bare RetroArch and it's not that easy to setup. It also can't launch Moonlight AFAIK and does not have a native way of loading Kodi if you're into that. Lakka is reliant on its libretro cores to launch apps, so you can't just add executable scripts to it like you can with EmulationStation, only the content compatible with the cores it has (like ROMs). The goal of Lakka at this point is to create some sort of game console OS first and foremost, so there's no room for different things.
If you want to use Lakka with Kodi, you can, however, dual-boot. The easiest way is with the images built by Matt Huisman. I'd recommend the LibreELEC one since it has less fluff. You can get the free version from
Vshare Mac version.
I personally like all three projects (Lakka, RetroPie, Recalbox), but I'm considering using the Matt Huisman Lakka + LibreELEC image just to try Lakka out. Some people say RetroPie and RetroArch are intimidating to use, but I haven't had many problems with them.