Most people expect ECB rates to go up. According to the futures market, ECB base rates will end 2010 at either 1.25% or 1.50%.
If you fix for one year now only, you will loose 4.30% gross - 3.50% gross = 0.80% interest over the potential pay out from year 1 as part of a 3 year term deposit. Hence, only fix for one year if you believe that there will be a real hike in ECB rates/term deposit rates in 1 year+.
I think you won't go far wrong with the An Post 3 year term deposit rate if you can afford to lock for 3 years. Your choice.