i normall put T1 or T3, whichever you think may get the best results
its dead now but winmx used to allow downloads instantly (mxmonitor) to users who had T3 connection.
generally if its a p2p prog it wont matter, if its some major online gaming site then it might make a difference. at the moment 3MB connection is about the fastest you can get (yes i do know about Bulldog) but i think thats an exception to the rule. 2MB (same as i am on with NTL) is fast enough for me so i wont be chasing faster speeds and you will probably find the same to be true.
transfer rates of around 240kb/s does a 1meg download in about 6-8 seconds
you can try cable/dsl and if you have problems, change it to T1 or T3 (what has happened to T2) i would imagine T1 to be 1 meg, T3 to be 3 meg, as we are in between then its whichever works well, trial and error