It really depends on ur location, if you are closer to your exchange/node then theortically you could achieve the max of 24mb that adsl2 offers though that is highly unlikely as there are many factors such as congestion, network stability, quality of the modem ect...
Honestly I am very happy with cable as I couldn't get Adsl2+ in my area, what you really should be thinking about is download limits.
With high speed internet there is the tendecy to use your limith up really quickly. Im currently on a 10gb plan which is reasonable though more would be better.
I'm paying $29.95 a month and get capped to 64kbs after the 10gigs, thought about 65% of bigpond cable coustomers don't get capped due to telstra's stupid networking protcols, with people abusing the flaw in the system. 1 terabyte downloads a month??? ( According to whirlpool forums)
I havn't gone over my limit yet but will try 3 day's before the next billing peiord.
If you can get cable do it,