Casey, my preference between Sportlots, COMC, and baseballcardstore.ca is Sportlots due to the overall experience that includes inventory selection, card prices, shipping options, and ease of searches.
Recently I used the Box option where I purchased 545 cards from more than 30 vendors over a 2-month span. They charge you a fraction of their normal shipping when they send the accumulation to the Sportlots Box, and when you're ready to have them sent in one consolidated order you'll pay an additional shipping.
My cost for those 545 cards was $257.07 + $36.83 to ship to the Box (not to me) + $17.15 shipping to me when I was ready to ship the consolidated order. The savings is in the shipping where I'd have paid multiple times over for shipping alone if those same vendors sent directly to me. I've just started another order using this method.
If you have any questions please feel free to send me a PM or post here.
“Aslan didn't tell Pole what would happen. He only told her what to do. That fellow will be the death of us once he's up, I shouldn't wonder. But that doesn't let us off following the signs.” - Puddleglum in The Silver Chair by C. S. Lewis