Its down to what you think looks better, will be value for money and fits your head better.
The e-vents are small but have a huge lense so you can see everything, it comes with 2 lenses stock, 2 peaks, bags etc etc etc, everything you could ever need
The i3 (if its the same as my normal i3) comes with a peak, a bag and thats it.
The i3 series have incredably hard lense change (well compared to other masks) whilst the e-vents it basically snaps into place.
The i3s have soft ears, the e-vents have soft ears
e-vents have 2 lenses (one thermal 2 pane, 1 thermal coating)
i3's have a HD lense which is thermal coating
Its what your more comfortable wearing - I suggest you try both on before you buy though