Cisco is always a safe bet.
Kentrox Q-Series QoS routers are also effective in certain applications. However, ADSL can be troublesome given its asymmetrical characteristics (high speed downstream, slower upstream). ADSL provides little in the way of guaranteed bandwidth, and ISPs typically resell ADSL residential service at a 25-60/1 ratio (subscribers to available bandwidth).
The best approach to your problem may be 2-fold. I would recommend first considering SDSL or other form of symmetrical broadband Internet service, which provides a more reliable and consistent downstream/upstream connection. Many providers also differentiate their DSL offerings by offering "business-class" options. These options typically provide guaranteed bandwidth, limits on cell loss/packet loss, reduced latency and jitter (delay variation). Admittedly business-class options are more expensive but at the same time, you're getting more in the way of (better) service.
In the end, neither SDSL nor ADSL are necessarily better at QOS as it is a function of the higher protocol layers running over DSL to begin with. However, because ADSL Internet is primarily targeted to subscribers who are looking for low cost Internet access, high speed downloads (i.e. web site access, content downloads, etc.) with less need/concern for upstream bandwidth, they offer little or no QoS. Without true end-to-end QoS, your best bet is to pursue as close to a full-duplex connection with minimal latency. Then and only then does good quality QoS hardware come into play.
(Crossing my fingers more providers begin adopting Resource Reservation Protocol (RSVP) so we can all realize the dream of true end-to-end QoS.)
