The Bose QC35 IIs are simply a classic. There's absolutely nothing wrong with them, and if you have them, there's almost no reason to upgrade to the new Noise Canceling 700s.
However, if you're in the market for a new set of ANC headphones, you should definitely be looking at the Noise Canceling 700s instead of the QC35 II. In this case, you should only be looking at the QC35 IIs if they're discounted much lower than the 700s.
The headlining feature of the Noise Canceling 700s is the headphone's 11 different active noise canceling (ANC) modes versus the traditional 3 step ANC from other headphones, including the QC35 IIs. Traditionally, you have: off, maximum noise cancelation, and some middle ground to allow ambient sound mode.
While the Noise Canceling 700s aren't the first pair of headphones to offer this type of ANC, it's one of the few out there. Other headphones that come to mind are the Sony WH1000XM3 with its adaptive ANC feature and the Microsoft Surface Headphones with its innovative dial design.
Bose QC35 II with Android phoneSource: Android Central
Speaking of design, the Noise Canceling 700s finally adopt gesture-based navigation. Swipe up or down to change the volume, backward or forwards to go back/skip to the next track, and double-tap to play/pause or answer/hang up a phone call. This is in stark contrast to the Bose QC35 IIs, which had the standard physical button navigation.
One of the only downsides to the Bose Noise Canceling 700s over the QC35 IIs is that the new 700s do not fold compactly. This means the carrying case and overall footprint of the NCH 700s are much larger than the QC35 IIs.
Bose Noise Canceling 700Bose QC35 II
Charging cableUSB-CMicro-USB
Battery life20 hours20 hours
ANC levels113
Bluetooth version5.04.2
Bluetooth audio codecsSBC, AACSBC, AAC
Foldable designNoYes
Navigation designTouchPhysical buttons
Ambient noise modeYesYes

What's better?

Well, both the Noise Canceling 700s and QC35 IIs offer a relatively neutral sound signature. With the QC35 IIs offering a more treble boosted sound signature. This means that songs with sharper, higher-pitched vocals and other instruments like drums could sound piercing and fatiguing. The Noise Canceling 700s tames that down quite a bit while also slightly boosting the bass for a richer and defined sound signature.
White/silver Bose NCH 700s in handSource: Bose
The Bose Noise Canceling 700s are the way to go if you've been eying a set of ANC headphones from Bose. They are more modern with a better overall design, USB-C, and a more customizable ANC.
Unless there's an incredible deal with the QC35 IIs (or even the original QC35s if you don't care for Google Assistant or Alexa), the Bose Noise Canceling 700s are the headphone to get when comparing your two Bose options. Unless, of course, you're looking for a more foldable headphone, in which case the QC35 II takes the cake.