Me first it seems...
Firstly, heaps of reviews on these two boards so make sure you read them.
Dundee is my fav of the shinn line up for carving, smooth riding at lower to mid speeds (and fast but it gives good feedback even at those speeds) real tactile with a lot of feedback to the rider, although I am spewing I have never got on a Super Shinn now they have discontinued it and replaced it with the ultrasonic (and by all my readings is completely different and has no more monk feel to it, why? Who bloody knows, why wouldn't you keep as much monk as you could is beyond me..oh well I digress).
I'm sure cauncy will elaborate on the monk if he feels the need.
For real surf carving...as close as you can get to not being on a SB, the mako is my experience is the best. The Dundee is awesome but it is a traditional TT in every sense and after a while as with all Tts you will get that back leg burn if you are going down the line etc. but if you just want to hoon around and take some short waves and jump a stuff...more in the freeride vein then the Dundee is better.
The king is an even better carver than the 150, even closer to a SB feel and bloody good strapless, but man its so damn heavy. If you do jump it, don't go crazy or you might start pulling intercostal muscles like I did.
Another thing, the mako has none, zilch, nada flex. So even though the huge concave and rocker gives you an awesome smooth ride (although some say that can feel a little dead/dull and is some respects they are right) especially between say wave sets, in the real choppy stuff, like crazy choppy sht, that lack of flex can be a pain. Come down from height hard, and say you have redirected wrong and haven't put in a loop to soften the blow it can hurt.
Also to add to this, the mako is not a great load, pop and booster, the back end squirrels out at high load at speed (this can be reduced with technique a bit and having mutant fins in), but the Dundee will offer you much better load, pop and boost potential for true freeriding. That being said you can still jump well enough on the makos, but nothing like a Traditonal TT. Some have argued in other places it is a technique thing, but fck technique I just wanna ride. Gotta be easy or fck off in my opinion.
So do you want to 'surf' in a more traditional sense on a what is essentially a weird looking TT, or do you want to carve, freeride, play around in the waves etc, then the Dundee. Remember the Dundee will also be good on super flat days to....just saying....

What is sure you are looking at two great boards. Me, I'd keep the SB for Surfing and the Dundee for everything else. Spray in the face is not synonymous with any of the shinn boards I have used. That mako, none whatsoever as you can adopt a more upright stance as the rail engages earlier with little heel pressure due to the huge concave. If no spray is paramount than the mako wins here, but hey who doesn't like to be sprayed in the face now and then...
That's what she said...