The Camry Hybrid (TCH) is very reliable; I've had mine for one year and 22,000 miles and there have been no problems whatsoever. The only maintenance ever done was oil changes every 5000 miles, and occasional tire reinflation. You can see I only average 33.5 mpg lifetime, but I drive pretty aggressively and deal with alot of stoplights. Extended highway drives at 80 mph yield 36-38 mpg, and 90 mph gives 34 mpg.

I have not driven an Altima Hybrid (NAH) though I'd love to. Nissan is not known for their reliability, however, but Toyota isn't known for creating sporty cars (not recently, at least) so maybe the Altima drives better.