Which one sounds more real?
Well........
Depends.
Soundfonts are usually shit compared to the large orchestral libraries like GPO or QLSO or what-the-fuck-ever acronym that comes out, however these large orchestral libraries [which come in VSTi form] cost a lot of money.
You could stick with soundfonts, though VSTi are cooler in my opinion, especially considering how much more flexible they are.
On the OTHER hand, soundfonts/samples may sound more realistic because they ARE, they're just sampled from a real instrument which may or may not work when sequencing, as opposed to physical modelling used in things like FL Slayer [which is supposed to sound like a guitar if you haven't noticed].