Define best? Point is that it means many thigs to different people.
Distance of the Avalanche Pass option over Algonquin without Iroquois or Wright's would just be under 12 I think. (I did the three & it came out as 13.3) It seemed a lot harder than the 14 mile day I did in June thou over Ike, Pierce & Jackson in NH
Trip does provide great alpine summit & super views from Avalanche Lake shores & thru Avalanche Pass.
Porter & Cascade offer two peaks & not too hard of a day. The classic trip of Rocky Peak Ridge & Giant from 9N I think would be over 12, both can be done from 73 in under 12 miles but invovles climbng down & back thru the Giant/RPR col which is fairly deep.
A couple of other suggestions:
for a short trip, Hurricane (3,694 feet) offers a bare summit great views
The trip up Big Side over the Brothers offers a ton of views from the lower two Brothers ledges & from Big Slide. (I'm in the camp that thinks the view of Gothics from close by is better than the view from Gothics since you can't see the slides from the top)
A loop over Sawteeth & Gothics would fit the bill too. (might be a little longer when you factor in the road walk but those are easy miles.)
Colden I think is under 12 too & can be done as aloop past the lakes & thru Avalanche Pass also.
Just too many great hikes to choose from.