There are any big differences but they are on the inside. The iPad has a resolution of 1024x768 and the iPod 960x640 The iPad has an a5 processor and the iPod (4G) an a4 which is a big difference in speed.
This seem small differences but it is really big if you look at the quality of the screen. The iPad can pop up more beautiful images then the iPod (4g).
iPod (touch, of course) It's many cheaper and you have more great games, and you can do it in your pocket. Except KR (I do not want that it comes to ipod, the screen is to small for that)
Me thinks that everyone is choosing iPad because it's bigger. Me thinks the iPod is better. But, it's the only one I have, so, yeah. I like it better seeing as it's more portable.
Personally, I'm a Droid fan, and find this conversation somewhat jarring, but I'll endeavor to answer from a purely technical standpoint.
An iPad is really only good for two things: reading an e-book, and typing an email. The size is the main factor in this. An iPod, however, is actually pretty good for multimedia (of any kind), internet (I'm going off the Touch generation onwards, here) and applications (the Apple App Store is kinda cool, too).
There's also the problem of how flimsy the iPad looks. If you were to drop an iPod, for instance (don't look at me like that, it happens) while fumbling for the headset jack, and it hits the floor - it'll survive pretty much intact. I wouldn't trust the iPad to take the hit in the same conditions (and, be honest, we've all got little cousins/nephews/nieces/daughters/sons/annoying little people who'll knock it over, or drop it at some point) and come out looking the same. Unless it's got a protective casing, in which case - no, I'd still go with the iPod, on the grounds of structural integrity. There's nowhere for the shock to go on the iPad except straight to the screen, which breaks. And you kinda need that.
I'm starting to ramble. Like I said - Droid fan, but iPod.
It depends on what you intend to do with your Apple Product. Ipods don't have to be Ipod Touches, I favour my Ipod Classic since I'm an audiophile. I like its portability, since it fits snugly into my pocket. I've tried out the Ipad a few times, and games work great on it, plus it's easy to organize your work life and reply to emails. But as a daily tool to carry around? I'll pick the Ipod. Coupled with my Iphone, I can play games, check up on my social networks and have music, which is good enough for me!
iPod seems to be more portable, but iPad seems to be faster and clearer because of the higher resolution. There isn't a massive difference between the two, Apple makes good money by hardly changing their products and then releasing them for a hundred dollars more.
ipod is heaps better usually dont break if you drop it but if you droppa ipad they just shatter has happened to heaps of my mates even when theyve just fallen off a bed or somthing :/