It kind of depends on what you're going to use them for.
Ipods are great for people who merely want to listen to music and play with applications. (Also, I've heard that they've made applications to make your iPod more like a phone, but I'm not positive.) Unfortunately, if you intend to go on java-based websites, they can tend to be slow or they won't load the site at all, I speak from experience. Apple's good with virus protection, so that's not going to be a major problem. They also have the capacity for "automatic updates".
Tablets are fun little gadgets, and they're pretty much faster than iPods. But, again, it depends on what you're going to use the tablet for. They're great for surfing the net, but not for online gaming.(I don't mean games that require downloads or anything.) Depending on the brand, virus protection might be required. Also, the brand determines whether you can set up automatic updates, or if you even have the option to update in the first place.
Netbooks are faster than the other two, USUALLY, and are better for online gaming. However, you don't get the applications Tablets and iPods get. Also, they require a bit more maintenance and updates on your part.
Hope this helps with your decision!