Amir is still a better bowler than Shaheen. This is reality. Shaheen disappears as soon as he fails to get a wicket in the starting overs. Amir is a multi-dimensional bowler who can bowl at any phase of the game.
Shaheen is usually effective only in the initial overs, he doesn't create much chances in the middle overs and usually gets thrashed in the death overs.
Amir OTOH, was more effective than Shaheen in the initial over, just like Shaheen he doesn't create much chances in the middle orders but it is very hard for the batsman to hit him bcoz of his back of the length deliveries and he is also excellent at the death, so I would say Amir wins this. I have hardly seen him giving 8+ rpo
Shaheen is a one dimensional bowler but Amir has the versatility to utilize conditions well. That's why you can expect a good spell from Amir throughout the innings while Shaheen is only effective with the new ball