T1 will give you better latency in a lot of cases from you to the exchange, but it's most likely negligible unless you are scalping and/or trading a lot of size. If you go that route get a point to point T-1 to your broker, which is distance $$$ sensitive.
I think this has been covered before so search.
Maybe you should tell what you are trying to do? Are you a high frequency scalper trading size? If so T1 may help. If not probably not a big deal unless you high speed residential options are poor.
If you download pingplotter dot com and ping a server close to your broker, depending on where you live, you should be under 90 milliseconds, if in the continental US. I just checked and from Denver to Chicago I am 50 today, but avg. around 6-80 which is fine. If you are in Europe pinging to America you might be 200-300 milliseconds which is normal.
The big auto bots collocate at the exchanges to make latency next to zero and prevent the # of hops your ISP routes traffic.
One other advantage of T1, and I used to work in telecom sales, is that when the network goes down business grade customers get brought up first, because you are paying more. That said reliability is fine for almost all nowadays.