I need to go to Dublin for two days then edinburgh for three and brussels for two in that order. Should I rent a car and take ferries(do they exist?) or boats and trains or simply hop on a bunch of planes. I guess I am looking for that "unknown best way" to accomplish this in a short time and within a reasonable budget.
There is no "unknown best way." But given the distances air probably is your best choice. Work the budget airlines for their schedules and fares.
Check whichbudget.com and skyscanner.net for flight comparisons. Some times, the major airlines will offer comparable deals to the discount airlines on competing routes, but they'll have better schedules.