The Bose QC35 is commonly recommended for open office work. They recently released a new Series II ($350). They aren't too different from the Series I which is discontinued but you may still be able to find some places for less.
Bose also has variants on this model, such as a wired one, as well as their top end in-ear headphones that are similarly recommended.
One thing to note is that active noise-cancelling in general isn't super great for conversation type noise. You'll probably have to combine active noise cancellation and/or noise isolation with some sort of audio playing to really not hear the office talk.
Anker also just came out with an ANC over-ears that look competitive for our use case for $100. I haven't tried them myself yet but am planning to.
[1]: https://thewirecutter.com/reviews/best-noise-cancelling-head...
[2]: https://www.amazon.com/Soundcore-Wireless-Cancelling-Headpho...
If you are trying to cancel out office noise, definitely go with over ear headphones. They are more comfortable for long wear periods
One thing to consider as you are deciding- in my experience noise cancelling headphones block out distractions better when actually playing audio. If you want to work in total silence, even the higher end Bose’s won’t get you there, as you can still make out the noise.
They work pretty well at blocking out sound and use a removable AAA battery and use a user-replaceable cord, so they should last you a bit longer than a few years.
I'm thinking of experimenting with 3M Peltor X-Series Earmuffs https://amzn.to/2AL91c7 though these are earmuffs, not headphones. It may be a nice backup for when there's just too much noise.
Noise cancelling headphones do a good job with "regular" noise; not so great when your neighbor is hammering something in his garage. Earmuffs are better for that kind of noise.
https://www.amazon.com/Cancelling-Bluetooth-Headphones-Micro...
But when I got QC35, it changed my perspective on what was possible with noise cancelling technology. Also they are really light and comfortable. I wear them 6+ hour continuously at office. And with music at very low volume I cannot hear anyone in the office.
If comfort is a big reason when you pick your headphones, if you have big ears or glasses like I do, then this is the way to go.
Audio quality is meh. I tried out my friends Sony WH1000XM2 and it has way better audio quality.
They cost around €220,-