There's an enormous amount of information on this at the Equipped To Survive website.
Remember it's not just the kit you're bringing along (or have on/around your body), but also the training you have had in handling it that makes the difference between living and dying.
A long while ago I thought that the ordeal was over after a successful ditching. But the statistics (from said website) show that in only 10% of ditching accidents, there are fatalities from the ditching itself. Typically because the plane is not landed under control. But once the initial ditching/egress phase is over, 50% of the people involved die from hypothermia. So once you're on the water the ordeal is just beginning.
I then did a maritime survival course which taught me a great deal about the practical aspects of surviving after the ditching. And there's a lot more to survival than just pulling on a piece of string so the liferaft inflates, after which you step aboard for a G&T.
At the end of the day, it's a risk/cost/reward thing. So far I have settled for a life vest, a drysuit (ex-dingy sailing type), a signal mirror and a rescue streamer. I'm still contemplating getting a PLB. All that stuff is carried on my body so I'm sure I can take it with me when getting out.
A liferaft sounds fantastic, and it is if you can deploy it properly and get in without difficulty. But there are a lot of drawbacks to it, and things that can go wrong. You really need to have had some serious training to use it properly.