For adsl2+ any of the supported routers really, its more down to what router works best on what lines.. and its not always the same.
For example the 2Wire routers are considered very good for long lines, but not so good for shorter lines.
Those on shorter lines seem to do well with the Thomson/ST routers. Broadcom based netgears work well, and the Billions also seem to get good reports. It really is sometimes a case of suck it and see.
On my own line I tend to find the Broadcom based routers work by far the best... plus these routers are often the ones that you can get the most stats from.