For me definitely 2 choices...
AH-1W - got a ride in one once when deployed on an LPH, adrenaline rush is the word! Also the sight of one of those blowing a target out of the water was simply awesome... a white dot in the Mediterrenean suddenly became nothing...
The next would be the CH-46 ... I flew medevac with the Navy and this was definitely the cadillac as far as ride... smooth and stable.. the versatility was unmatched as well... some of the 46's we flew in were circa Viet Nam... and still pounding away.
I flew a few CH-53's and they were like riding rodeo style, nothing but bucking and rocking... not to mention the scary hydraulic fluid leaks... the crew chiefs always said if you didn't see the leaks THEN it was time to worry... but all in all you had to be impressed with the size and power of em...