What are some pairings of systems in your view that go really well together, (past and present) and in what way?

Switch 2 and PC. As somebody who craves 60FPS and loves to emulate older titles, Switch 2 just doesn't cut it: There's no 60FPS Final Fantasy VII Remake, there's no 60FPS nor (high-quality) CRT shaders for the classic NSO library, etc. Meanwhile PC isn't easily portable, it's a hassel to set up at times, and doesn't run many Switch 2 exclusives. Essentially all of my gaming needs are covered with these two systems.

There were so many competing experiences in the seventh generation that it made sense to have a 360, Wii and PS3. But Wii and one of those other two in particular was an awesome combo. You could get the majority of third-party games that gen whether you had a PS3 or 360 and you could play Nintendo games and any third-party games that interested you on Wii.

A neo geo pocket color and an xbox one

With this combo you get a quality on the go experience in color and tv and sports

My current setup:

Switch 2 + Steam Machine

Switch 2 for portable games, Steam Machine for AAA games.

Yeah while all three consoles that gen were awesome and worth having, either a Wii + 360 or a Wii + PS3 was a great combo, they were do different and each offered unique experiences.

SEGA Saturn and PlayStation esp for RPGs. PS1 had the most but Saturn was no slouch and if you had these two into that genre (and can read Japanese for Saturn) you were in heaven. 

PCE Engine/TG-16 and SEGA Genesis + SEGA CD/PCECD for Shmups. PCE Was the best shmup machine of it's era. Over 100 of them more than any console of the time. Genesis was no slouch and had some amazing exclusives like MUSHA. Gaiares. Gleylancer and more. When they did share ports. Some played better on PC Engine/CD or on SEGA CD like Lords of Thunder. 

8th gen I liked having a Switch and PS4. Both systems got a lot of good ports of arcade like games or indies. I liked having my choice of PS4 for better performance or portable on Switch. It was nice to have that choice of better performance or convenience without the TV. As much as I love 90s gaming. I do not miss when the portable of a game was...Mortal Kombat for Game Boy. Switch and now Switch 2 you get the full experience. You may lose some frames and/or a lower resolution but the core game is the same. 

I usually want a handheld system for gaming on the go combined with a powerful machine for big games in the living room.
Two different powerful consoles never made sense to me. Only for people that have time to play exclusives from each system.

I sort of liked the Wii360 thing that was going on during that generation. Mostly because I was a die hard Nintendo fan at the time and liked anything that made more people go for a Wii. Even if I later probably enjoyed the PS3 more than at least 360 and maybe even the Wii.

If I would like a pairing with that is highly complementary I would stay in that generation. Either a DS as a handheld for all the unique and crazy games as well as great gaming on the go and a PS3 for big games. Or shift them up and Have a PSP for the "normal" games and a Wii at home for crazy unique stuff only playable on that thing.