Is is better at today's rates when the euro is at all time low..to get euro in US before leaving or incountry at the airport upon arrival in Lisbon ?

Unless you are a gambling person or can predict the rate changes between the dollar and the euro, plus take into account the unfavorable rate for buying euros outside the Euro zone, just take you ATM card and withdraw the money as needed when you are there. All major airports have ATMs for your convenience.

Others can comment on the bank charges levied by your home bank for withdrawing money from a foreign ATM.

And the answer for Lisbon is no different than the answer for anywhere else in the euro zone. There are many, many threads here on this subject.

i was going to buy all in US or at Lisbon airport...

"Buy" suggests going to a currency exchange counter. That is more expensive than taking money out of the ATM. To minimize costs further, check to see if if your local credit union levies any charges beyond the 1% VISA (it's the company doing the conversion) imposes. Banks like BofA charge higher fees.