I think it depends on what you're doing or who it's for. as far as home consoles, the OG Xbox and the Wii have been the best basically their entire existence because they've had the largest communities working on stuff like that. we're at the point now that the wii has 32x emulation and pretty much everything from the ps1 running well on it.
for someone dipping their toes into retro stuff, or for a kid I'd say as home consoles go a Wii U is probably the best bet. I always tell people with young kids that's the way to go. you can load a drive with 300 Wii U games (maybe a few choice DS or 64 VC games), and another for the vWii side with the full library of everything console up through the 4th gen, and then most of the ps1+64, handhelds up through the 6th gen, then the full Gamecube & Wii libraries, most emulators allow wii remote for lightgun games, on top of all that some arcade, SCUMMVM for point and click games with the wii remote, some old PC emulation, ports of various FPS's, Sonic Mania, etc. on top of that it's got 4 player support out of the box for everything for co-op play, HDMI out for ease of access, and can be set up in a way that are pretty much un-fuckup-able and with box art for a kid, your not much of a gamer/tech savvy partner, or dumb friend who's at your place a lot to just turn on and use.
on the handheld side, for the same type of person/kid it's a preference based toss up between a 3DS/2DS, Vita, or any one of those modern cheap handhelds that play up through the Dreamcast well. largely for the same reasons as I mentioned for the Wii above. it basically comes down to, do you want Vita games, to play DS or 3DS games in a non-shitty way, or do you want a little more powerful home console emulation on the go sacrificing those things? give it a couple years and there will be a more powerful common chipset in the majority of those cheap handhelds and some more dual screen options and they will probably be the standard best option.
for someone with a CRT i'd go with the original wii for the correct 240p output on emulators, and video output on wii/gc games (they're very slightly off on the wii u) and actual GC controller ports for dance mats or gba connectivity with zelda, animal crossing or crystal chronicles. or someone just more in the scene or wanting to go further a mini pc with a frontend to handle more systems. there are other good options too, the OG Xbox is largely interchangeable with a wii for many of the same pros but I think the wii/u is a little more bang for your buck as far as what you can do with it variety wise. a ps3 or xbox series devmode is a great option too.
every system I have is modded to some degree (or I have everdrives or ODEs in them) and I set them up for people all the time and it really just comes down to preference or what you want. I will say I am pretty firmly singing the praises of the Wii(U) and those retro handhelds particularly for people with kids or getting into retro games because there is nothing cooler than basically having access to every game ever made up to a certain point on one device. a pc or mini pc is the best or most complete option but that's almost a different conversation.
