You can barely even classify this as a kitchen island, but we do have to start somewhere. Moveable islands are more like portable prep areas that you keep to the side of the kitchen rather than featuring prominently and permanently alongside your primary counters. The butcher block trolley is a familiar type of rolling "island."
Pros: Cheaper and easy to move in and out.
Cons: Moveable islands tend to roll. These wheels tend to become unlocked with surprising frequency. When locked, these types of wheels do not provide enough grip on floors, especially when cutting or mixing on them.
Freestanding Island - non-fitted
These islands differ from the portable, moveable islands, listed above, in that they do not have wheels on the bottom. More importantly, they actually strive to emulate a "real" kitchen island.
At just under a meter, they are the right height for prepping food. They don't have the annoying tendency of those rolling islands to slide away when you're trying to cut something.
Pros: If you want something resembling an island, this is the way to go.
Cons: You may be surprised at the smallness of these islands. 1.2m long tends to be the maximum length. Is that big enough for you?
It's got four legs and a flat top, so it's a table, yet it's positioned where the island usually is, so it must be an island. It's nothing more than a table that's used as an island for preparing food.
Pros: Easy to bring in and "install." Easy to remove if you don't like it (it's not attached to the floor). Using a table as an island also gives your kitchen a certain Martha Stewart charm, but in a good way.
Cons: It's just an extra flat surface--no fancy frills, no extra storage, no sink, no backsplash. It's just a table.
Fitted Kitchen Island
An island built out of pre-existing materials: a base cabinet (or two or four) topped with countertop material.
Now this type of built-in island, which is fixed to the floor, is considered to be permanent. Usually, these islands range in size from 1.2m up to as long as the countertop slab size allows(without a join) or as long as your space allows (with joins). Stone countertop sizes range from 2800m up to 3.2m.
Pros: By far, the easiest built-in kitchen island for a homeowner to build but not the cheapest.
Cons: The back side, which is ordinarily not seen in cabinet form because it faces the wall, must be covered with a veneer or finished piece.
Fully equipped Kitchen Island
Alternatively, if your kitchen has space for it, you can marry two base cabinets back to back. Also, you'll need to have countertop material cut "to size."
The fully functional kitchen island does everything that the primary countertops do: electrical, sink, drainage, and ample countertop space.
Pros: This isn't just "auxiliary counter space." This is almost an entire second kitchen.
Cons: Your costs have skyrocketed due to the addition of plumbing. The sink's supply and drainage do not conveniently tap into the main sink's lines (in the same way that a dishwasher, located next to the sink, will do). Your island's lines run into and under the floor, eventually meeting up with main supply and drainage lines.
Dual use Kitchen Islands
Is it a kitchen island for cooking or is it a kitchen island for eating? It can't quite make up its mind, so it has decided to be both. This island combines the two functions but still delineates them so that cooking is done on a lower level and eating on a higher level or even a lower, dining height level.
Pros: This type of island is ergonomically correct. Optimal counter height for a standing cook is 900mm. Best height for a bar top is 1.1m and seating height of 750mm.
Cons: By providing dedicated eating space, you reduce your cooking space. There is no way you can prep food on that upper deck, even if you wanted to. With a flat cooking/eating island, you could always impinge on the eating area if you had to.