Lakka is probably 'closest' to the hardware level (with Vulkan support and minimal overhead), and has overclocking management built in (but not on the GPU level) - so it would be 'best', except that it isnt.
Atmosphere (/Horizon) with native homebrew is still the usability king. (Quicker to launch, quicker to get back - when something crashes, quicker to charge, wireless controller support is best, ...) Which beats out all other aspects for the most part.
Switchroot (Android) beats it out, where 'more commercial emulation' solutions are still better (think higher resolution output on PSX games (which the switch core currently doesnt support), better Nintendo DS emulation, better Dreamcast emulation). The major downside of Switchroot currently is charging it (10% charge per hour, if you are not charging in Horizon (Atmosphere), and that general navigation isn't great due to the touchscreen still being registered "too sensitive".
Also setting brightness levels and power profiles isn't as comfortable. Linking the controllers via bluetooth all the time also is a hassle.
As soon as you are in emulation though (and have your controllers mapped) - its great.
Where purely performance on Retroarch is conserned, Lakka probably wins out (spoken with Dreamcast emulation in mind), but then - that isn't so important.
So everything _but_ Dreamcast emulation in Retroarch basically runs well in Atmosphere (Horizon) as well - so you tend to go with that.
And for Gamecube, Dreamcast and Nintendo DS emulation, Android (Switchroot), has maybe the more interesting (commercial) emulators currently (Redream (Beta), Drastic, Dolphin, ...) - so that might even win over Lakka at that point. But then Lakka maybe has better battery life than Switchroot and maybe a little more performance for Gamecube titles...
So if only performance were concerned, Lakka would probably be the winner.
But in daily use its probably a distant second or even third (third in my case), with Retroarch on Atmosphere (Horizon) winning all the way.
Also - with sys-clk you get minimal GPU overclock in portable mode in Atmosphere (Horizon) (only ever overclock the GPU by one step here imho), which is important in some cases - and which the other platforms dont have.

Its not a dealbreaker in any direction - but its nice to have (and know about).

(Usually only important for PSP emulation.

)