Rouge/assassin, but as I'm "only" 26 hours in, I literally just unlocked that tree, so haven't invested any points yet.
So I use a bow and stealth my way to a good vantage point and just shoot people a lot
Blackwall uses sword and shield. I've tried to focus his skills on defence and taunting. Don't know what he offers more than Cassandra, but she's just a bit annoying and he has a nice beard.
Iron Bull goes in and hits everything, he's just there to do as much damage as possible
Dorian is there to flirt and occassionally send some spells around. I'm not sure if he's necessarily the best mage, but I like his fire and lightning spells. I still haven't gone to unlock Viv and I was never convinced by Solas
I haven't experimented with my party that much. Cole and Sera haven't seen the field at all and Viv is still somewhere in the countryside. It's just too much of a bore to keep them all well equiped
Dragons still do terrify me though. I'm level 12, so I guess I shouldn't be too far away from taking them on. But I am curious what I should be spending my money on. I tend to get nice progression of armour and weapons through looting. I have also picked up a fair few designs to craft add on items, which I have been sticking on. I haven't had much trouble with these methods, but I'm only playing on normal and playing quite thoroughly, so am appropriately levelled