I’ve always carried one premium card and one no-fee card and always seems to work out well, although those cards shift over time. Currently it’s the Amex Aeroplan Reserve and the CIBC Costco MasterCard. Everything goes through the Amex unless it’s a retailer that doesn’t take Amex.

In practise, Costco trips are the only time I use the MasterCard, although it’s always useful to have (especially overseas) for those times I encounter places that don’t take “American”