I haved personally owned several of the boats (Roll-up, HP, and RIB) and as is true of any boat, each one has its positives and negatives.
I will venture out on a limb and tell you what to buy for your boat: a High Pressure Inflatable with an outboard engine.
The RIB is by FAR the best performer and the most stable... but hauling it up on davits and towing it behind is a bear. We lost about a knot on our 38 pulling our RIB... so I can only venture a guess that you would lose at least that too (assuming you are not in large seas). With large seas, you will get a lot of jerking that can be overcome by placing a snubber on the painter (which we use now even on our HP)... but it is still a real pain to use. Thus, I think a RIB is best suited for much larger boats (maybe 40 feet and up) that are less affected by the weight and can handle RIBs being hauled up on davits a lot easier.
The Roll-up is by far the ligthest and easiest to handle. It will quite literally fit into a bag and you can stuff it in the Lazarette. We used this for quite some time on our 32 foot boat, and it works. However, the boat is difficult to handle (no keel, so steering is hard), stepping in and out of the boat with the spongy floor is awkward (especially in rolling seas/beach), and you are very limited on the motor size you can use. If you dont have much money, this is better than nothing... but if you don't mind investing a bit more:
Buy a HP Inflatable. They are expensive, but a good compromise between the two. It is not as stable as the RIB, but really is not a problem. It does not deflate and store as eeasy as a Roll-up, but you still have the option when you want to do it. You can put a larger outboard on it and get pretty good performance (plane out), but not as quickly or as smoothly as a RIB. Still, for your size boat if you have the money, you will end up being happiest with it.
I will go against the previous reccomendations for a sailing dink/hard dink. I have not owned a Walker Bay and not sailed one, but I have given the a close examination and I personally would not make it my primary dink. If you really want a sailing dink, there are much better ones made. But the weight and instability (and cost, of a decent one), is more than most people will be happy with... especially on a 30 foot boat. I have been in smaller sailing dinghies many times, and I will tell you they are a bit squirelly and tender. They are fun to sail... but still not the best choice for a primary dink (again, in my opinion).
If you have specific questions on the model, etc that I have owned and run, you can reply back here or PM me.
Good luck shopping and have fun.