Given how many novels you read, your best approach is first to find the stores that sell what you like at the best price. With the exception of genres like science fiction and romance, the best place is probably the Kindle Store on Amazon.com. Note that all ebook stores have geographic restrictions, but the Kindle store requires you to own a Kindle or an iPhone/iPod Touch to buy from them.
If the Kindle store is best, then get a Kindle 2. If any other store looks good, then you have more choices.
If you intend to get ebooks from a
lending library, then MOBI ebooks are readable (with some effort) on the Kindle, but there are many more Adobe ebooks at lending libraries. See what ebooks your local library contains (if any). Many ebook readers, other than the Kindle, will read Adobe lending library ebooks.