Would there be any significant difference in recording quality between the following:

1. Zoom H4N

2. Focusrite Scarlett 2i2

I would be using them with a Rode condenser mic to record vocals and an acoustic guitar.
The Zoom is better for stereo live/location recording. The interface is better for multitrack recording. Different tools for different jobs and for mating with a Rode mic I would choose the Scarlett.
"Your sound is in your hands as much as anything. It's the way you pick, and the way you hold the guitar, more than it is the amp or the guitar you use." -- Stevie Ray Vaughan

"Anybody can play. The note is only 20 percent. The attitude of the motherfucker who plays it is 80 percent." -- Miles Davis

Guthrie on tone: https://www.youtube.com/watch?v=zmohdG9lLqY
You could also consider using a multitracker as your DAW for a 3rd option.

The H4Ns are really only any good as audio notebooks & getting a rough recording of practice sessions etc, I wouldn't want one for anything more than that.

Either way, read the stickies.
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Quote by PSimonR
I'd go for the Scarlet. The pre is real quality. Unless you really need something you can carry in you pocket - but then with all the accessories you need to make it work...

Have you had any latency issues?
Zoom R16 and R24. Both portable stand alone. Both daw interface and surface. Only time I have any latency issues is if I'm pushing the PC hard with about 20 plug ins, kontakt etc. The PC gives up before the zoom will.