Internet Access

I work for a small business that will soon combine 3 locations into 1 and need high speed internet access for approx. 50 users. We currently use ISDN for our access but our President wants something faster to accomodate us all. We are a moderate Internet user, mostly downloading updates to programs and email. Would going with T1 be the next best leap or should we consider something else like DSL or Satelite?