
Flexispot
E7 Pro
Affordable and stable, but assembly can be confusing.

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Get a Walnut 2" 70x30 live edge block for $500 from Etsy and then get a Deskhaus Peak Pro and grab the free Rubberwood surface for fun.
Uplift is usually seen as the golden standard. Very stable and seem to have good quality parts and good customer service. They "include" (built into the price) a lot of gifts (gimmicks) like a foot hammock, t shirt, etc into their purchase, which actually convinced me to keep shopping. Flexispot is often posted because they run permanent sales and give people discounts/cash back for posting reviews. Their design/quality doesn't seem too good. Deskhaus has good reviews and seems to be slightly better quality-wise than Uplift, though they aren't as big of a company. Their customer service also seems less polished, but still good (again, small company). I wanted a 4-leg frame and they were significantly cheaper for the Peak Pro ($725) than Uplift ($919) for just the frame, so I went with them. Uplift will probably be fine whether you want a 2 leg or 4 leg. If you want to save some money, getting a deskhaus frame and a top from Home Depot, Lowes, etc will probably end up being cheaper and a better overall desk.
At sitting height, pretty much any half-decent standing desk will be stable. If you're 5'4", 2 leg desks from a good company should still be stable at standing height. If you're 6'4", 2 leg desks will probably be unstable at standing height. I have a 4 leg desk and it's perfectly stable even at maximum height. I have to intentionally push it to see any monitor wobble. During normal use, there's nothing.
Slightly over your budget, but look at the Deskhaus Peak Pro. You can get it with a free rubberwood top. edit- maybe not. I just ordered one, and that code didn't work. Maybe they ran out.
Yeah, most likely. They still had the banner up advertising the code when I ordered, but it didn't work. Luckily I found a different code that saved me $50, so I still feel like I got a good deal.
My Deskhaus Peak Pro with 3 monitors (2 34" UW + 1 27") has no wobble with all of them on monitor arms. This is for both sitting (26") and standing (41") heights. I think the Deskhaus Peak Pro and the new Flexispot E7 Plus Max are the best you can get for least wobble?
I think the Peak Pro you can get for about 800 shipped. Around the same for the E7 Plus max? Worth the extra $100 imo. Mine has been problem free and no wobble. Plus, these standing desks will last years as they all have 10-15year warranty. Just need to change the desktop if you want something new. Worth the extra $$ if you spend 5-6+ hours a day at it.
I just set up the deskhaus peak pro (it has four legs) and it has no discernible wobble at any height, though for some reason my monitor would pick up a little motion and I put a foam block under it on the side (like a second little "stand") and it's TOTALLY solid. I'm 6'1" so was told I needed a four leg model. But at like $800 it's not cheap.
I'm 6'1" have the peak pro and it's solid. My monitor sits on it on a stand in its center, I did put a block under one end of it because it moved a TINY BIT (that fixed it), but yeah, I feel like I'm pretty sensitive to movement and it's solid.
Our Peak series has wedges for lateral stability. I should have mentioned the Apex Pro Max too but thats almost double the price so unless you want a rock....it's hard to justify. https://preview.redd.it/5tndrmv5hegg1.jpeg?width=450&format=pjpg&auto=webp&s=f71e53aefb8419ee1967ec5f84d52119de3de062
Okay, I'm just gonna tell ya then....The wedge makes it more stable...period. But where it's more stable, I'd be willing to say, 80% of the people using are not going to experience it. Being manufactured stateside is the sole reason it's more money. Get the Peak Pro and rest easy.

Flexispot
E7 Pro
Affordable and stable, but assembly can be confusing.

Uplift Desk
2-Leg V2 Standing Desk
Durable, stable, but expensive with poor cable management.

Dezctop
Bifrost Series
Modular design with great cable management, but pricey accessories.

Flexispot
E7 Plus Max
Very stable and durable, but assembly and cable management are tricky.

Secretlab
MAGNUS Pro
Excellent magnetic cable management, but expensive and gamer aesthetic.

Ranked #1
Uplift Desk - 2-Leg V2 Standing Desk
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Ranked #1
Flexispot - E7 Plus