Porter or Air Canada?
 

I've seen dreadful reviews on both, but Porter's were from a few years ago. Have never flown Porter, flew AC several times without issue, but it's been almost 10 years. Choices are limited into Halifax, particularly if I don't want two connections or to fly out of BWI.

It would help to know where your trip will begin.
Finding dreadful reviews for any airline is quite easy. Read them with skepticism.
There are several distinctions between Porter and AC. Biggest is that Porter does not fly jets, relying instead on a fleet of stretch Dash 8 propeller-driven craft. They are configured to allow a comfortable amount of leg room. However, capacity for carry-on bags is more limited. These can be checked on the tarmac, which means they are delivered fast after landing. Porter also is based at the so-called Island airport in downtown Toronto, named for WW1 fighter ace Billy Bishop. AC has limited service to that airport but most of its Toronto traffic goes through Pearson, the country's biggest, now with a commuter train downtown. AC has a wide array of planes in its fleet, including some Dash aircraft, depending on the route.
You do not mention WestJet, Canada's second-biggest airline.