USB 2.0/3.0 vs Soundcard Line in & S/PDIF

Novice question here, which interface is faster, less cpu usage and latency?
Thru USB 2.0/3.0 Soundcard line/S-PDIF? thanks!

So which way would you go if you had to choose between USB or PCI/e (soundcard)?

would think that PCI or PCI/e would be the best if latency is a big issue for you.

 
Round-trip latency for the Babyface, Fireface UC, and Fireface UFX is 4.9ms at a 48-sample ASIO buffer size/44.1k.
That's better than most PCI/e audio interfaces.
If you're running a fast i7 based DAW, you can sustain substantial loads (glitch-free) at that setting.
 
It's really down to making a good choice.  Good with a proven rock-solid unit (that's known to provide low RTL)
Almost anything PCI/e will have pretty low round-trip latency.
Few USB 2.0 audio interfaces provide low round-trip latency but they do exist (FTU/8R and RME units).
A handful of Firewire units also provide low round-trip latency (RME, MOTU, Steinberg).
 
Make a good decision... and you'll have low RTL (regarless of the bus)

I had used a USB soundcard a while back (creative SB Xfi) for my Laptop, I was using it on an online karaoke website (face palm) lol, and there was latency on my recording? another thing I noticed is there's this noticeable noise (data noise?) whenever I tried to record something..

 
Typical USB audio interfaces suffer from high round-trip latency... so the above doesn't suprize me.
If you were using an RME Babyface... you'd have great fidelity, rock-solid drivers, and very low round-trip latency.
 
The best advice I can give you is to go with a unit that's a proven rock-solid performer.  A unit that's known to deliver reliable low latency performance.  If you have the budget, RME (any of their units - PCI/e, Firewire, or USB) would be a great choice.