If you buy at a B&M shop, the BEST time to buy smokes is during an event IMO. You get some freebies added on and you often get raffle tickets to win crap like lighters, hats, ashtrays and even cigars. Its worth it to hit up local events.
I generally buy online at CI. I'm a cheapass, so I will normally check what deals they are slinging, and I also get their what seems like daily emails with deals. Most of the time, they are hard to beat and aren't always advertised. When I'm low on smokes, I buy what fits my budget. Most of the time I get "brand" samplers full of assorted sizes and/or cigars from the brand. I tend to check the deal of the day, which will give you free shipping if you buy that, which saves you 5 bucks.
ymmv
T