Mountain bike or road bike?
Mnt bikes have gone to 29” because once rolling they roll over large obstacles without feeling too much. But remember thT the bigger wheel is a little harder get going out of the hole. That being said, gearing is lower so with the rear cassette able to have more gears (10-12) you can have a really small high gear cog all the way thru a really large low gear cog, say 11-50ish with a single up front, so not needing 3 front chainrings. Doubles and now singles up front are the way to go.
Disc brake units are far superior to the ones ten years ago. Shimano leads the way.
Speaking of disc brakes, a lot of road bikes now have them but unless you live in or ride in mountains why bother?
I have a new Trek Domine that has urethane dampers built into the seat tube/seatpost juncion to absorb vibes as does the head tube/stem junction up front. Shimano Ultegra is redesigned n lighter, more durable to offer old Dura Ace quality at Ultegra prices.
The BIGGEST improvement to road bikes is the move to 28c tires on wider rims. Running 70 lbs of pressure vs the 110 I use to run. That with the suspension damping seat & head juctions makes the bike more comfortable, rolls over rough surface that is the norm today, which actually decreases rolling resistance making the bike faster n comfy at the same time. They are lighter too.
You can get a really great road or mnt bike @ $3000& up
If you’re going mountain bike, make sure you go with a tubeless setup. That’s the best bang for the buck