Full share of any one stock. So investing in something like appl is easy. If you on have $15 put it in a stock like that and you'll see a better long term return.

Penny stocks are fun but your growth is very small. I would rather put $5 in something like appl than $5 in a penny stock. If appl jumps 1% on apple stock you've made more on the return than 10% return on a penny.

If you want to see some decent return look at sticks in biotech trading around the $1-$3 range. Huge risk but great opportunity for growth.