Best sailer as a KAYAK is the Adventure - it is the fastest and the daggerboard gives it the best all round sailing performance of all the Hobie KAYAKs.
If you want the fastest Kayak-based sailer the the Adventure Island TRIMARAN is the way to go (either single or tandem). These are faster because they have a bigger sail and outriggers to support the extra weight aloft. They are also extremely stable and (I can personally attest to this on the single-set AI) a very wet ride in windier conditions.
I have an AI which I most frequently sail in KAYAK mode i.e. without the outriggers and with the small Hobie sail; to do this you need to make an adapter to allow the small sail's mast to fit the roller reefing cup on the AI hull (an easy an inexpensive task - some parts from Hobie, a broken windsurfer mast and some epoxy basically). Once you have the adapter you can roller-reef the small sail which is worthwhile benefit. The standard Adventure hull has a different mast base to take just the small sail - some people have modded the rig to allow this to roller-reef too. Don't even think about trying to use the AI sail without the outriggers
Personally I get far more enjoyment out of sailing my KAYAK than I do from sailing my TRIMARAN (or either of my other two sailing boats) - it is dead simple to rig, much more challenging, less full-on (i.e. wet) and it is more engaging... but it is slower and only for light winds. (In really light winds you can fly a mainsail and jib which adds a whole new level of complexity, skill and challenge).
Re the relative stability of the Hobie Kayaks when sailing - basically the wider boats (e.g. Outback) probably will feel a bit more secure but as sailers they are outclassed by the Adventure hull and in none of these boats are you immune from being capsized by wind action alone if you overcook it. Personally, as I have said, if sailing is what you want to do the Adventure (or Island) s the only one to go for because of the daggerboard.
Re capsizing: I have been in for an unexpected bath on 3 occasions in probably 6 or more years of very frequent trips so it doesn't happen often but it does and will happen if you push it. While I would prefer not to get dunked I have never felt too stressed about it when it happens: on only one occasion did the boat completely invert; I have only lost a fish, a knife and a water bottle as a result of capsizing because I keep everything I can tied to the boat; on each occasion I just righted the boat, climbed back on board (after collecting up the flotsam), sorted out the mess of tangled lines & fishing gear and went on my way... I am also lucky in that I don't sail in freezing waters but with the right gear you should be OK - even if you get wet & cold as long as you can get back to shore before hypothermia sets in !
If you are really concerned about stability some people add various smaller outriggers (Hobie sells them) to their Adventure hulls to provide trimaran stability whilst using the small sail... personally I have never been tempted by this because I have a trimaran but prefer the feel of the sailboat leaning to the wind.
Hope this helps.