I like AGNC, and I've owned it for a little over a year now. My personal opinion is that it has a place in a well-balance dividend portfolio, composing perhaps less than 10% of one's assets.
The ~20% yield is nice, however, they often finance it with new share issues, which drops the prices, as right now the payout ratio is greater than 100%. The company's business model is borrowing at low interest rates, high leverage, and investing in guaranteed mortgages - it's a good business for the current economy that we're in with low interest rates. However, once rates rise, I think the yield will drop, and the price will tank. So, invest wisely, and use less than 10% of your assets in this type of investment.