A Keurig versus Nespresso really is apples and oranges--the drinks they make are very different. Keurig as you know is about basically drip coffee and tea. What's great about it is the huge variety of coffees, including flavored coffees. However coffee and tea are the only things it does.
Nespresso on the other hand is about doing espressos. On the plus it's a quality machine, it's drinks taste good, and it has the convenience of a pod system. The main downsides are 1) most of their machines are quite expensive 2) selection is limited to 10 espresso varieties and 3 lungo (think Americano) varieties, and 3) if you've ever had a properly prepared espresso from a high end espresso machine, you'll know there's still quite a gap between what a pod system like the Nespresso can do and a really good espresso machine can do (when properly operated).
Keep in mind though that to produce superior espresso means grinding your own very fresh beans, perfecting your barista skills, and rigorously maintaining your machine to keep it clean of coffee residues. Truly a pursuit only for the dedicated.
Anyhow, if you're looking for easy espresso, I do think a Nespresso is a good choice--probalby your best choice for very convenient and consistent results. If you want to make lattes and cappucinios, their two most appropriate models are the C190 and the D290. The D290 is more expensive (499 versus 379 for the C190), but it has programmable water dosing and an auto-froth attachment (it works but I can do a better job by manually steaming--auto-frothers generally over-foam the milk and don't get it hot enough).
Another alternative in the game of convenient espresso are machines that can handle a kind of espresso pod that's similar to a coffee pod, however there aren't many machines that do a good job with those and results aren't as consistent as with the Nespresso; on the plus side though there are more varieties of espresso pods available than Nespresso capsules, and machines that can do pods can do ground coffee too if you want to try your hand at that. A downside to espresso pod systems is that you have to find the better pods; there are plenty of pods out there but not all are really good ones.
A good all around espresso machine that can do pods is the Bodum Granos. Another is the Solis-SL70. The Bodum is the better looking and in my opinion better built of the two by a good margine, but the Solis does at least as good a job. Both are good at steaming.
Anyhow, if you want the greatest convenience for espresso with the least machine machine maintenance and the most consistently good selection of coffees with no hunting for them, I'd go with the Nespresso. If you want the widest selection and the ability to try your hand at brewing from your own ground coffee, I'd get a Bodum or Solis. If you mainly want drip coffee, get the Keurig or one of the other pod brewers.
On the other hand, if you're totally sure you love espresso and the quality of your drink is important above all, get a really good espresso machine and grinder and learn how to use them skillfully. Once you've tasted a really fine espresso there's no looking back. If you want to try that path and don't know where ot start, visit the coffeegeek.com website. There is tons of information including zillions of reviews.