Audio interface: Internal PCI(e) or External USB/FW

Hi there!
I’d build new DAW.
I thought about some i7 config (e.g. 4930k)
My question is: which type of sound interface shall I prefer?
Internal (e.g. RME DSPe AIO) or some external on USB2/3 or FireWire (e.g. Steinberg/Yamaha MR816CSX)

Is it true, using the internal card gives more stable system with lower latency against usb or fw?

technically yes PCIe will be better.
not always the case however
its all about the manufacturers ability to write drivers.
RME PCIe or USB/FW are stellar the PCIe difference is 32 buffer vs 48 not a huge difference.

you need to decide how many I/O you need, Midi, Mic pres (onboard or boutique)

Not too much I/Os. Usually 1 mic, 1 line in, 1 MIDI In/Out.

I will choose RME HDSPe.

The other consideration is that an audio interface will typically endure through at least a couple of computer changes, so having an external unit based on USB, especially if you are not using anywhere near USB’s bandwidth, may be more sensible.

On the PC side, PCIe will probably endure for a few more years, but Apple has dropped internal PCIe on the new Mac Pro, and as UAD2 Solo, Duo and Quad users have discovered on the new Mac Pro with external Thunderbolt PCIe bays, newer PCIe systems may not be compatible with older cards.