I picked the 4 because... well.. because I'm a bit weird :P
I don't know exactly why, but I see that number as a sign of good things (and the 5 as something bad). I'm looking for numbers everywhere (even in things where no numbers are involved) to see if anything is good or bad. Whenever any numbers are involved (phone numbers, license plates, dates, ...), I start calculating to see which number "it really is". And when I recall my earliest childhood memories, I find that even back then I did things that were 4 (if this makes any sense), or fours bringing me luck.
Stupid examples: I won a scooter race when I was in preschool. The kid who started te race counted "One, two, three, go!" In my mind, "go" is basically the 4 (coming after three, being the fourth word, etc.).
When I played Warhammer 40k, I was totally obsessed with Khorne (Blood God, the Lord of Skulls, the Chaos God, sitting on a throne of bones - hey, I was a teenager!). Guess how happy I was when I learned he has that thing with the 8, which is two times 4. Me, the 4, joined Khorne and all things became 8.
I'm a huge Formula 1 fan. When Lewis Hamilton came into F1, I became a huge fan of him. I never really liked Sebastian Vettel. When Formula 1 changed how starting numbers work (they were based on championship position, now they're chosen by drivers), Hamilton picked 44 (Yay!) and Vettel picked the 5 (I knew it all along!). When the young Charles Leclerc started winning the lower categories (GP3, Formula 2) I thought there was a great talent on his way to Formula 1. Guess which number he picked when he finally arrived... 16, which is 4x4.
Another one: 256 bit? 4^4, of course. There's a 25 (5x5) in it, but that's beaten by 4^4 and by 2+5+6=13. 13 is 1+3=4.
Well... As I said, I'm a bit of a nutcase there.