I've used both, the loop and the nail.
I like a nail knot much better. You can get a knot tying tool at WalMart for six bucks. This will make a perfect nail knot every time in only ten seconds.
Like Frank said, you don't have to make your leaders. Just go to WalMart and buy any mono leader you like for $1.99!! and any tippet on a neat tiny spool for $1.99.
Most leaders now come with a loop on the end...... and twice the price! LOL And almost all the fly lines come with a loop. I don't like the loop and always cut it off. Even my $100 Sharkskin! True you will lose a half inch every time you put a new leader on, but after ten years of lot's of fishing, a inch won't make any difference at all.