Add me to the list of happy MOTU AVB users. I have an Ultralite AVB and it's working flawlessly for me. Very low latency, solid drivers and great sound. 
 
 

Jim Roseberry
Many USB audio interfaces have issues with 3rd-party USB3 controllers.
(Liken the situation to using a non-TI chipset Firewire controller with Firewire audio interfaces.)
 
Prior to the Z77 chipset (and derivatives), literally *all* USB3 ports were provided by 3rd-party controllers as USB3 hadn't (yet) been integrated into the Intel chipset.
 
With current generation motherboards, many have additional USB3 ports (in addition to the Intel USB3 ports).
These are provided via 3rd-party controllers.  Avoid using these with USB audio/MIDI interfaces.
 
To address the OP's question:
You won't go wrong with RME
MOTU's new AVB line is very good
 

Had to find this out the hard way. Interestingly, I found the lower the latency, the less crackling. Anyway, I'm springing for a PCI-E Fireware card. I have a Motu Ultralight Mk3.

My new computer is an HP Envy 850, and I believe it has the Intel USB 3.
 
I'm considering the USB 2 MOTU (88, 896) and the Presonus Studio 192.  I'm definitely interested in hearing what's working well among the newer offerings. 
 
Is there anything compelling about the AVB line?

schwa
My new computer is an HP Envy 850, and I believe it has the Intel USB 3.
 
I'm considering the USB 2 MOTU (88, 896) and the Presonus Studio 192.  I'm definitely interested in hearing what's working well among the newer offerings. 
 
Is there anything compelling about the AVB line?

Nothing really, it's just the latest interface that's hot.
 
In your case with your USB3 PC, you''ll need to get an I/O card for either AVB, USB2, or Firewire - depending on how you choose for an audio device.

schwa
My new computer is an HP Envy 850, and I believe it has the Intel USB 3.
 
I'm considering the USB 2 MOTU (88, 896) and the Presonus Studio 192.  I'm definitely interested in hearing what's working well among the newer offerings. 
 
Is there anything compelling about the AVB line?

You might want to take a look at the SOS review of the Studio 192.
http://www.soundonsound.c...resonus-studio-192.htm

schwa
I'm considering the USB 2 MOTU (88, 896) and the Presonus Studio 192.  I'm definitely interested in hearing what's working well among the newer offerings. 
 
Is there anything compelling about the AVB line?

 
If you're after lowest possible round-trip latency...
Thus far, no USB3 audio interface yields lower round-trip latency than the best USB2 audio interfaces.
RME Fireface and MOTU AVB series both offer great sound... low round-trip latency... and solid drivers.
 
If you want round-trip latency lower than 4.3ms at a 48-sample ASIO buffer size (44.1k), your only options are PCIe or Thunderbolt (running PCIe via Thunderbolt drivers).

After some more research, it seems I may be able to continue with my old MOTU 424/2408 setup.  I have a PCIe x16 slot available, and it seems like I could get a PCIe-424 card.
 
I didn't think that PCIe x1 card could be used in an x16 slot, but the "internet" tells me it's possible.  Some others say if you install an x1 card next to an x16 card, it ruins x16 performance.  The newer card would be less expensive than most interfaces I am considering.  But at $295, they're not giving them away.  If the new card would affect graphics performance, that's no bargain. 
 
Do the PCI 424 products have comparable latency to the current USB2/firewire/AVB products?  I could install a less expensive (PCIe) Ethernet or firewire card and go with something newer, but I'd prefer not to spend a grand on something new if what I have will work well.

schwa
After some more research, it seems I may be able to continue with my old MOTU 424/2408 setup.  I have a PCIe x16 slot available, and it seems like I could get a PCIe-424 card.
 
I didn't think that PCIe x1 card could be used in an x16 slot, but the "internet" tells me it's possible.  Some others say if you install an x1 card next to an x16 card, it ruins x16 performance.  The newer card would be less expensive than most interfaces I am considering.  But at $295, they're not giving them away.  If the new card would affect graphics performance, that's no bargain. 
 
Do the PCI 424 products have comparable latency to the current USB2/firewire/AVB products?  I could install a less expensive (PCIe) Ethernet or firewire card and go with something newer, but I'd prefer not to spend a grand on something new if what I have will work well.

The number "x" refers to how many PCIe lanes the slot uses.
 
Audio interface controllers are all x1.
Fast PCIe SSDs are x4
The only peripherals that are 16x are video cards.
(Even with video cards, there's little to no performance compromise running via 8x)
You can install a x1 or x4 PCIe card in an x16 or x8 full-length slot.
 
As to whether a PCIe x1 card affects the performance of an adjacent card:
It depends...   
If the slots don't share PCIe lanes (nor IRQ), performance won't be affected.
 
The MOTU PCIe 424 controller is one of the best performers when it comes to lowest possible round-trip latency.
 
 

Thanks Jim for such a considered response.  Any tips on how I could find out if there are shared IRQ or PCI lanes?
 
From what I've gathered my new PC has a crap-ton of lanes, and that IRQ conflicts are less common in newer computers. 

Most modern Intel CPUs provide 40 PCIe lanes (4790k, 6700k, 5930k, etc).
The 5820k provides 28 PCIe lanes... but is otherwise essentially the same CPU as the 5930k.
Now... don't let that number make it seem like the 5820k is a "dog".
 
Unless you plan to run multiple x16 devices (at the moment only video cards are 16x), you'll most likely do just fine with 28 PCIe lanes.
 
Your motherboard manual should detail which slots share resources.
Of course, you can also see this (after the fact) by looking in Device Manager.