As to which Business is better it's a matter of opinion, but TK is highly rated.

The bigger thing to keep in mind here is that an Aeroplan award in business on TK will cost about $80 in YQ (which is fuel charges, taxes etc.), while an Aeroplan award in business for the same route will carry almost $1000 in YQ.

...so you're *much* better off flying TK whether IST is your final destination or not.