If you are buying term life insurance, it is pretty much a commodity product, so go with where you can get the cheapest rates. I find it is easy to shop at intellequote.com
If you have a complicated mrdicalplan history and need someone to haggle with underwriting, then maybe use an agent.
You can always cancel a term policy. But there are no guarantees you can get a new one as you age, or that the price won't be higher.