Unless you're going for a cheap off-brand tablet, 9 times out of 10, a 7" tablet will be cheaper just because it's smaller.
If you're going for a 7" tablet or a less expensive tablet, go with the Nexus 7, hands down. Great price, great specs, and updates straight from Google.
If you're going for a 10" tablet, I think the Asus Transformer TF300 is the best option out there at the moment. There are higher-end Transformer models (Prime, Infinity), but they're both pricier and don't provide the bang for your buck that the TF300 does in my opinion. Not only do you get top-notch specs, but you also get the best support in the industry from Asus, who is almost always the first to push out new updates. The TF300 has had Jelly Bean for a couple weeks now when the Verizon Galaxy Nexus still hasn't received it. Asus is also extremely responsive in fixing any issues that might arrive. And a big plus with any of the Transformer models is the keyboard dock that turns the tablet into a full-fledged Android laptop. In the dock, along with the keyboard, you get a full-size USB port (a great thing for external drives and accessories, including game controllers), a full-size SD card slot, and extra battery life. You're looking at up to 16 hours of battery life between the tablet battery and the keyboard dock battery (and the keyboard dock charges the tablet battery). The TF300 also has a microSD card slot and HDMI out.
So, in my opinion if you want a 7" tablet or a more affordable option, go with the Nexus 7. If you want a 10" model that offers more features and the best support available (outside of direct support from Google), go with the TF300. Ironically enough, both of those tablets are manufactured by Asus. Google went with Asus for the Nexus 7 because of their quality, success, and the support they provide.