LEGO

I have quite a bit of experience by now. I had heard increasingly good things about Lego competitors, and wanted to get my own impression. In addition to that, I was growing more and more frustrated with Lego's decreasing quality (and still am, btw). So that's why I got my first non-lego sets.

My experience so far has been pretty positive. If you do a bit of research beforehand, it's pretty easy to avoid the crappy stuff.

• Piece quality: everything that uses Gobricks pieces is gonna be extremely high quality, higher than Lego in most regards. The clutch power is stronger than Lego though, so stacking plates can be a bit dangerous. Gobricks pieces are used by a lot of brands, including Mould King and Funwhole for example. For other brands, a bit of research will tell you what to expect in terms of brick quality.
• Set quality: how well the sets are designed of course varies wildly, but there's lots of really awesome stuff out there. Another field where a little research will go a long way. There is a lot of stuff you would never get from Lego, for example Funwhole only does sets with fully integrated, nicely thought through custom lighting kits.
• Legality/Morality: There's lots of brands that just do their own stuff, which is nice and unproblematic. Some brands, like Mould King, apparently sometimes use MOC designs without the creator's permission, which I try to research beforehand and not buy those sets if that's the case. Some use IPs like Star Wars without proper licensing, or flat out steal set designs from Lego, which, idk, not that great but also I don't really care about big corporations losing money over that.

Overall, I would say it's a little harder to know what you're getting compared to Lego, even within the same alternative brand. You have to put in a little more research effort, but imo, it's absolutely worth it, not even only looking at the price.

Edit: Just noticed I should probably provide some examples of what I've actually tried so far. Give me a sec.

Edit 2: Alright, here's a couple examples so far:

• Mould King Botanical Garden. This was the first major set I got, really happy with it. It's a MOC, but officially licensed from the designer. Looks awesome, lots of details. Construction is a little flimsy at times, but it's Gobricks pieces so it still holds together very well.
• Funwhole Lakeside Lodge This one is just awesome. Looks amazing, interesting build. Also Gobricks pieces, although I would have preferred the lower clutch power of Lego pieces here since it's a lot of plate stacking.
• Sembo Flowers Got a couple different flowers from Sembo, they were all good. I think they're also Gobricks, but not 100% sure - the clutch power at least had no trouble keeping together the somewhat delicate builds. There were a couple of 1x1 half round tiles that seemed to be slightly mismolded here, but everything still worked.
• BlueBrixx Pro Reichstag Berlin First non-Gobricks set in this list. The design is cool, but the brick quality was a bit lacking, quite a few mold problems in there. Still held together and looks good, though!
• Forange Triceratops Egg Very cute build, no problems with the pieces.
• Cobi Boeing 787 Cobi produces their own bricks (in Europe, no less!), and has lots of special shapes you don't get from Lego, as they are much closer to model building, with basically no emphasis on play. There's no stickers in this set, and the prints are incredibly high quality, no comparison to Lego at all. It's all more specialized, though, so not that great for people who like to take apart their sets and build something else with it. Their tiles don't even have grooves for the sake of a sleeker look, so they're really hard to get apart again.
• Panlos Mini Street View Cinema Nice design, again, nothing to complain about with the bricks.

Got a couple more, but I'm getting tired of listing these. Open for questions if anybody's interested!