Again, there is so much to consider and so much tablet pcs out there but the bottom-line is, make the best choice based on what suits your needs for the device, not on what the hottest thing out is. That's the key to finding them at a good price. The OS right now it's no secret that Apple and Android are the 2 big players here.
Android is surging upward for sure, but Apple is the number one right now in terms of OS and applications, and will be for a good while. With that said you need to make decision on which one is right for you. Some Applications may be available for one but not the other. The Android market at this point is known more for quantity over quality whereas Apple personally reviews every app before it hits the market.
If a particular port is not available on the tablet you are looking at then you can pick up an adapter for pretty cheap. Of course a USB port and 3.5mm jack are standard.Being able to plug in your tablet to a projector or a television is something that those with a business use for a tablet are going to require without a doubt. VGA and HDMI are the mainstays in that regard.
If you're willing to pony up the extra cash for a 3g connected tablet then you can count on having a connection wherever you go. Normally this will run you an additional monthly fee, even a contract for this service. If you live in a home with an internet connection already and mainly plan on using the tablet in your home perhaps you can forgo getting yourself hung up into contract. Bluetooth is also something that can be useful. Not only does it allow you to transfer data wireless, you can also plug in peripherals wirelessly as well such as keyboards, mice, even headphones. Of course no mobile device is complete without GPS and is indispensable for those on the go and needing directions.
This is just a few of the many features and things to consider when looking for tablet that is perfect for your needs.