Depends on the lake and when you will be fishing. A lot depends on context.

Most people fish lakes that are pretty much surrounded by houses and are well traveled. Also most people fish during relatively warm weather. Under those conditions a full life jacket is ridiculous. Wear one and your going to sweat, chafe and it will get in your way until you take it off. It will end up on the bottom of the boat and be forgotten and neglected. Unworn it won't do you any good if you fall in. No matter how much it costs, USCG approvals, and the buttload of survival equipment it may contain. After some time, even if you later put it on, odds are it won't help you after being kicked around and neglected.

Assuming any or all of that is applicable odds are your going to far better off with an easy to wear automatic compact inflatable model (Type V PFD) that will remain reasonably comfortable under a summer sun and over a light jacket. What it lacks in protection it more than makes up for by being worn.

This article covers the major points but it is from 2002 and the general standards, reliability and functionality have improved since that time.

http://safetycenter.navy.mil/MEDIA/ashore/issues/winter01/automatic.htm

These life jackets are popular with offshore sailors who will wear a PFD for thousands of hours and who often have no prospect of swimming to shore.

Of course if the lake you fish is fifty miles from the nearest habitation, is seldom traveled, if your lake is near freezing because of the season or because it is fed by a glacier, if you like to fish during storms or shoot rapids to get to your favorite spots, then a more comprehensively protective vest and, perhaps, a certain amount of survival gear makes a lot of sense.