I prefer the proportionate, gridless style in theory, but I don't think that the SwSh trailer tackles it very well. The overworld looks rather generic with linear pathways, while LGPE make the classic Pokemon style more vibrant and immersive.
I naturally don't like LGP/E's style just because it is the same 2.5D nonsense that GF was pulling up until they finally really started pushing away from it with Sun/Moon. However, beyond that, it's hard to say. I do remember thinking that despite the awful style, LGP/E did look nice graphically (with some exceptions, like I remember the floor textures in a battle they showed looking really low detail).
I'm not too impressed with Sword/Shield. Sure I'm happy that the series moved away from 2.5D, but I still feel like the environments in S/S are still held back from some archaic "square" placement thinking (for lack of a better way to describe it on my end) and still don't feel very organic.
I don't think the graphics of Sword & Shield are quite finished yet, so I think it's a slightly unfair comparison, but in broad terms, I prefer the look of Let's Go. The colors feel more calm and natural to me (whereas SS has that radioactive grass and casts everything in a weird pink filter), and the characters/Pokémon blend in more smoothly with the overworld due to the textures on the models. I'm not really sure how to explain it, but the people (and objects like Poké Balls) in SS all kinda look like they're made of paper? Which is jarring to me, against the 3D overworld.
I feel like talks about graphics in general are kinda misplaced for this series, one that has lived most of its life on limited handhelds. Stylistically, its too early to say which I prefer because I haven't experienced the Gen 8 games yet. I liked the "atmosphere" of Let's Go and felt that it was fitting for what is a modern 3D Yellow remake; but for the series proper I've always leaned towards Colosseum's more gritty style, especially when it comes to Pokemon modeling or attacking animations. The effort put into those alone makes prior offerings feel almost lazy in comparison.
There are some things about Pokemon that lend better to an anime-ish style, and there are some things about the world's lore that would be better suited to something more realistic.
From what I've seen, I veer towards Sword/Shield, just because of the proper proportions. I also feel the lighting looks more realistic and atmospheric, whereas LGPE looked more plasticky. I still think though LGPE is leagues better with its colors than X/Y and Sun/Moon.
Though honestly, I really wish they would touch up some of the models. A few of them just look off, and the animations are still really boring, especially when compared to Pokemon Colosseum and Stadium way before them. I'd rather they focus more on life-like animations now, because the graphics are perfectly fine to me. (Just for the idle poses though. I think the attack animations are fine.)
I prefer the realistic portions of SwSh as well as the, for a lack of a better term, vastness. Let’s Go looks to me like a very polished gen 6 game in that the characters were chibi and the environment felt cramped and unrealistic, which isn’t very appealing to me. It didn’t feel like LGPE was taking advantage of the new and better hardware, at least in terms of the environmental models.
I kinda prefer the cel-shading of SwSh. The shading of LGPE is nice, but looks really weird on some Pokémon. The lack of textures on the skin of some Pokémon, think fur or scales, makes them look weird in the LGPE shader.