I have used dry yeast for many years with good results (and yes, having extra yeast, and of course hops, in the frig is a good idea). Only recently have I used liquid smack paks, to expand my experience (and tastes) in brewing. I have noticed a longer lag with the liquid yeasts, but never had one that failed. Some books call for salvaging and re-pitching the liquid yeasts, which is one of their advantages (tried once, but could not re-pitch in the recommended time). However, all-in-all, the dry yeast have always had a quick start and have produced good beer. I do believe some of me best brew batches were with liquid yeasts, buy I mainly use the dry ones because of their quick start and general reliability.
One reason I like the dry is that I do not have to plan real far in advance (my schedule gets tight sometimes) and can brew without the worry of getting the liquid smack pak started hours in advance