Welcome to the forums! Say "hi!" to Zorro for me ...
Asking for the kitchen sink isn't entirely unreasonable ... I always use my new knives in the kitchen to see how sharp they are and how comfortably they fit my hand for work, not just display.
Defense is more in the mind than the hand. Robert Heinlein wrote, there are no dangerous weapons, just dangerous men. If you expect a knife to defend you, you'll find it just sits there in your trembling hand while the bad guys all know what to do with theirs.
Any knife that can slice a melon or carve a turkey should do fine convincing a mugger that you're more trouble than his time -- and skin -- is worth. Unfortunately, you do have to be ready in your own mind to use it on him. Not a pleasant prospect.
What knife, what knife? You need a few very specific recommendations to begin with. For your first knife, avoid serrations. They are specialized, and you dont want more than a 3 blade, on which they will take up too much slicing length.
Check out the
Benchmade Model 705 - McHenry & Williams Small Axis Lock which goes for $105.99 but you may find discounted on our Exchange forums. The axis lock is very strong and is ambidextrous useful in a utility knife. The McHenryWilliams design is relatively innocuous.
A new possibility is the
Camillus/Darrell Ralph EDC (Every Day Carry) which is $49.99 in 420HC, a good steel, or $64.00 in 154CM, a great steel. Its not ambidextrous, but the integral lock is super-strong, and the handle is extremely ergonomic.
Another good choice would be
the Cold Steel Medium Voyager 3 Clip Point blade for $52.99.
Look at these, see what each has to offer, along with the variants, like tanto point, serrations, larger sizes. After a while, some of the logic of the different styles, sizes, lock types, and steels will begin to make sense then you can start buying too many knives, like the rest of us.