I've had all 4, tank and broot on live, scrap and stalker on HC. Stalker is far and away the best. I'd rate them Stalker>Tanker>Scrapper>Brute. Stalker's the only one you won't be ineffectually chipping away at bosses after everything that was pumping up AAO is dead.
As to the effectiveness of AAO on stalker, it's fine. Obviously it's not as noticeable as it is on a shield tank vs a non-shield but it's still extra damage for you and less for them.
Also I'd recommend you try skipping thunderstrike. It's just so slow.