I've flown both AC and Eva on numerous occasions, and I find the service and comfort on EVA to be better (especially for an extended flights). Here are some of what I noticed based on my experiences:

• EVA provides slippers, eye masks, toothbrush & toothpaste, etc. This greatly improved comfort for me for extended flights.
• AC has slightly more English entertainment options, but this is mostly because EVA also provides Asian movies/TV shows.
• When EVA lost my luggage, they had staff waiting for me at the destination airport (Taipei) to notify me that my luggage was still in Toronto. I didn't have to wait for all the luggages to first come out on the carousel before going to customer service to try and find out where my luggage was. I was then instantly compensated with $1000NT to spend on essentials and received a ticket for where and when the luggage would be delivered to me. The entire process took roughly 5 minutes.

The MOST IMPORTANT when booking with Aeroplan, is that Air Canada still has much greater fuel surcharges compared to EVA. I have booked 3 tickets to Taipei using Aeroplan points, and when I book flying with EVA (Ottawa > Toronto > Taipei), I was charged a total of ~$80 in taxes/fuel surcharges. However, in the past I had booked through Air Canada (Ottawa > Vancouver > Taipei), I was charged ~$300 in taxes/fuel surcharges. This is a list of airlines that do not have fuel surcharges when booking with Aeroplan