The 5i is a warmer, more musical sounding preamp then the 30. The 30 is slightly clearer sounding and slightly more dynamic.
I have never heard the 5i, but owned a VK-30 and 3i. Of the two I would give the nod to the 3i. I could not warm up at all to the VK-30. I won it on a contest at the Audio Revolution website and foolishly sold my 3i before it arrived. I only kept it a couple of months before moving it on. There was an upper midrange glare that rode along with the music that was very irritating, no matter what tubes I rolled in it. YMMV.