86box has more features, and the latest version comes with a frontend. PCem updates are long in coming, making its forks preferable (just like DOSBox).

I've used DosBox, VMware, VirtualBox, MSDOS(vm), 86box and PCem to run DOS stuff on non-DOS systems. I still do most with
DosBox, but for faking a "real" system, I've settled more on PCem. I found 86box tougher to setup and tweak, but it really
depends on what you are doing. If you need to get optimal performance/compatibility (like much gaming), you prob would do
better with the more capable/complex ones - I'm mostly just testing stuff I've written an typical old systemss, and
find PCem best (for me). I don't really care about slow release times - The systems I'm testing on haven't been "released"
in decades - so far not encountered any critical bugs which need immediate fixing.

So I scoped out 86Box recently, and was enormously impressed. It now lets you mount folders from the host system in the virtual CD-ROM drive which is a convenience I'd been longing for. I was curious if the mouse felt any better, and I didn't think so? But it seemed no worse than before, and about the same as PCem. I don't know, maybe my system isn't fast enough to benefit from that. I only have a 5800X3D. The shaders for 86Box are nice too. If you use the OpenGL renderer you can specify the GLSL shaders you want to use directly from the application. If you use the Vulcan renderer you can use something like Reshade to get really fancy.

Performance for me seemed the same as it ever was. PCem and just about any version of 86Box seems to max out around a P233 MMX for my host system. There might be some changes in performance on the margins, but I wouldn't expect a new class of performance out of any version of these.

I use 86Box on Linux because it has a flatpak available.

For networking PCEM only has 10 Mbit support while 86Box has 10/100 Mbit support.

Huh? No Gigabit ethernet yet? How comes?
Doesn't, for example, Intel Gigabit-Ethernet-Controller 82574L have DOS support?

I mean, 10 or 100 MBit/s isn't exactly much.
If you divide by 8 (Bit to Byte), it's about 1,2 Mbyte per second, or 12 MByte per second, respectively. On paper, without overhead.

In practice the bandwidth is about a bit it more than half of that.
So 700 KB/s (a DD diskette) or 7 MB/s. Not exactly quick.

Way back in the 2000s I found it funny that DSL was slower than transfer rate of a floppy controller.
Or that then-fast 10MBit cable internet connection was the maximum speed of an 10Base2 NE2000 card from 1987.
Even ISA bus from 1984 was faster than that (16 MBit/s theoretical).

Edit: I did’t meant to criticise the authors of PCem/86Box here.
I've just assumed that various network adapters had been emulated a dozen times in the past 25 years or so (in different projects)..

As far as I know, there haven't been any changes to 86Box's underlying emulation performance, so PCem should still provide somewhat better performance.