Wifi is the slowest way to transfer the the images but does have the advantage of not having to physically connect your computer or having to remove the card. So, if you don't have many images to transfer, this is definitely a good option. If you have a lot of images, it'll be a lot slower than the other methods. Also, if transferring a lot of files, make sure your camera battery can hold up for the duration of the transfer.
Using a card reader means you have to spend a bit more (i.e. purchasing a card reader). You'll also have to pop the card out/in each time, which might be a bit of a hassle for some, depending on the size of the card (especially if it's a microSD). On the other hand, the speed at which it transfers photos will be dependent on the card reader so the transfer rates could be quite good. (For example, if your computer supports USB 3.0, get a USB 3.0 card reader to ensure the fastest transfer speeds.)
When the camera is connected to the computer via cable, your camera is acting as a card reader. This has the advantage of not needing to have a separate card reader to transfer your images (and not having to pop the card out/in, though you will have to fiddle with the cable). One thing of note is that if your camera is older, it may be slower than a modern card reader. For example, if your camera is older and effectively acts as a USB 2.0 card reader, then it'll be slower than using a USB 3.0 reader. This could be a huge hassle if you're transferring a lot of files. It also drains your camera battery so you'll have to be careful that your camera doesn't run out of juice part way through the transfer.
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