Well, in my opinion all three of those classes are useful. I'm not sure that I'd say any of them is particularly more useful depending on how well you play it.
Bards can sings songs which benefit groups and raids by giving buffs of various kinds (2 at a time), and are capable of dd, dot, mez, slow, and other debuffing with damage songs. They don't do a ton of damage until higher levels, and soloing they seem more suited to kiting.
Rangers get buffs like SoW, small heals, the ability to cast damage shields, and root and snare mobs which can be extremely useful for both solo kiting and crowd control in teams. They do decent damage up close (especially when whirling blade stance kicks in), and get some serious range damage as they get better and more specific arrows to choose from for a given situation.
I won't say too much about Beastlords, because I haven't played with many at a higher level, but I did duo with one on my bard from 10-55, and it seemed like he was fairly durable, did comparable damage to monk/ranger, and had a lot of useful debuffs. And of course, his pet was very useful for handling an add until we could get to it.