My own preference is leaf. My experience of pellets is that they make the beer very difficult to clear. I find two problems with dry leaf. First, they tend to float, not saturate, and if this happens you'll not get the full aroma out of them. Secondly, they are much more bulky than pellets, so you can lose more volume when you decant.
I get round the first problem by scalding the hops first, so they are already wet when I add them. The second problem is something I've got used to - for me, much less of an issue than having a fine haze of hop powder in my beer that I can't easily get rid of.
You don't say what the volume of your brew was. For me, if I wanted a really hoppy beer, then for a 20l brew I'd want at least 100g of dry hops, probably more, and I would leave them in for more than 3 days - maybe 5 or 7, with regular agitation to encourage mixing and to break up any floating "hop cap".
Oh, and if it isn't bitter enough, then it's not down to the dry hops. Bitterness is determined largely during the boil, but also influenced by any late additions whilst the wort is still hot.
