It might be Torna but I won't cast a vote. I'll just talk about what I liked from both.
I like the world of 2 more than the world of 3. Alrest has history, actual civilizations, politics, people working all different jobs and lifestyles, and more fleshed-out nations. In that way it's a bit easier to be pulled into stories from its world more than Aionios's nothing but endless war and everyone's a soldier schtick. From there, I think I was compelled by the relationship with Lora and Jin. Their story feels like it stands on its own well enough. FR on the other hand just feels like a platter of fanservice. I mean, look at what everybody talks about with the story: the radio. It's about fan-service, lore drops, and capping of the current story arc, but I don't think it has as much to offer as just its own thing like Torna did. I mean it's there with Na'el, and she's an interesting character, but her story and relationship with her brother Matthew is drowning under the lore-heavy Xeno-series-wide connections bonanza. I guess I'm also so-so on Matthew whereas Lora's one of my favorite Xeno protagonists.
On the other hand, I do like the cast of FR overall better than Torna's. It's a bit of an unfair comparison considering Torna has to make 9 characters interesting, when FR only needs 6. Torna has some deadweight with Aegeon while FR gets to flex with grown-up Shulk and Rex. Though I do see the issue with making two of the six previous protagonists, and another two their children. I know posters in an older Xenoblade thread on here were disappointed with FR's focus on lineages and how it adds to the overall straightness of the game with the "and then they all coupled up and had kids!" thing, so I can understand FR's party as a bit problematic in that way especially with Linka and Panacea in the mix as well.
Gameplay-wise, FR really shines with the AP system. The checklist aspect of it is very fun and you end up engaging with more of the world than you usually do even taking out trash mobs you would normally run past and having to actually pay attention to the time of day and correct weather to find some monsters. That pippito that only appears when it's snowing on the Ragmos Desolation was particularly memorable to hunt down. It can feel like a band-aid to other issues that have gone unfixed though. Finding chests being fun now because you gain AP, doesn't solve the problem that 80% of accessories are still junk. The kits were good though.
They both have more focused gameplay than their base games and I think I might like the combat of both more than their respective base games. I like Torna's significantly more than base 2. FR vs. base 3 combat is harder to determine, but chain attacks were better. Character building systems on the other hand were abysmal in both. People rag on XC1 for not being as customizable with character builds as X and 2, but even 1 puts FR and Torna to shame. They both lose in that department.
Map-wise, they're both good in their own way. I like how all of FR's playable area is seamless with the Metroidvania-elements of building ladders, ether slides, and the like. The area styles were perhaps a bit simple, but I liked their flourishes. We start in a forest of red grass and trees at sunset which has a great vibe. Putting one of the Uraya trees as the chief landmark in the Aurora Shelf was a perfect touch and I love that you can see the pink leaves poking over clifftops in other areas, and of course, the Bionis Leg and Valak mixed with Tantal are memorable. Again FR does rely a lot on fan service. The final confrontation is at Prison Island and it can often feel like a trip down memory lane. But I'm not immune and can't deny I got emotional visiting Colony 9 and hearing the old music.
Torna's maps may not be as impressive. But I respect 2's general thing of not making interconnected maps and instead focusing on each titan as a separate biome which has its own strengths even if not as immediately impressive as a seamless world. Torna follows the same design but tries to make its new titan layered and a bit bigger than the base game titans. It's okay, but what stands out more is having a unique biome with the white sand dunes. Aurora Shelf and Ragmos feel like ordinary Xenoblade grass worlds, I mean Ragmos is straight-up Bionis Leg after all. But nothing we didn't already have in the base game. Aurora instantly recalls Rae-bel. I also liked Torna's visit to an older more wild version of Gormott. Remixing an area was a fun idea and I was slightly disappointed FR didn't let us do this despite seeing a lot of Cadensia in flashbacks and the ending. Both games also bring two memorable secret areas with Millennium Grotto in Torna and Headwater Cavern in FR, I loved both.
I think FR could've used one more area theme. The main overworld track is fantastic, but we hear it a bit too much. I wish the Red Forest could've had its own theme like the Lasaria Woodlands in Torna.
Future Connected beats both of them for best battle theme though