It depends on how much power (and especially torque) you intend to push through the gears. The old NuVinci N171 was rated for 5000W as long as you remained within the torque limit. The N360 and later models were rated for 2500W. That's more or less what the Rohloff hub is rated for, and it too has an input torque limit.
Rohloff is very expensive and has been so all along, but NuVinci hubs were in the $400 range when they were in production. A quick check on eBay right now turns up new old stock NuVinci hubs starting at $240 shipped.
If you want to use a currently manufactured gearhub under $300 with a mid drive, you're going to have to keep the combined pedal and motor torque within the normal range of what one person can do with an approved gear ratio. Otherwise, sooner or later you'll crunch it up. I did it to two Sachs 7-speed hubs in a row, without the help of motor power.
There's nothing wrong with Nexus 3 to the best of my knowledge, though its early predecessor the Shimano 333 hub was known to be weak. Sturmey Archer 3 speeds are known to be fairly robust until the drive dogs become a little rounded off, and then they're prone to skipping and false neutral gears.
I've never had a great deal of faith in Shimano Nexus 7 hubs, but I've had a couple and I've never been able to make one malfunction. (I have ridden them at body weights from 300 to 400 pounds.)
I wouldn't recommend SRAM i-Motion 3 or 9 speed hubs to anybody, for any reason. Likewise Sachs Elan 12 speed of you can even find one anymore.
Even though they're out of production, my highest recommendation at this point would be a new old stock NuVinci N340, N360, or N380. My older and heavier N171 hubs worked great with a BBS02 mid drive combined with my unusually large pedal torque, and they both failed only because the force of the hub-mounted brake overcame the side cover's locking tabs. (So if I did it again, I'd use a rim brake.)
The advantage of NuVinci hubs is not only their power rating which is applicable to e-bikes, but the fact that they're always fully prepared to transmit torque; they're never "out of gear" or partly engaged.
Second choice for me would be Sturmey Archer's heavy duty 5 speed hub, though I have no experience with it. I'd also consider using the SRAM Automatix 2-speed automatic hub. Mine has been faultless, though I've never applied motor power to it.
Over the last 20 years, I've really gone to lengths to substitute internal gears for derailleur gears. They make stronger rear wheels and their working parts stay clean and correct. But I have either broken or retired most of my gearhubs. It's really hard to beat the fault tolerance and robustness of a derailleur system with 7 speed cassette, when reliability is key.
