I use Dxtory, it's not free though. It's way better than FRAPS because it has many customization options.
It's better with memory but worse with hard drive space but that's mainly due to the codecs you use, you can use a codec that creates a smaller file but compressing that small file takes up memory resources. I play in 1080p but scale down recordings to 720p for the simple reason of saving hard drive space.
The standard Dxtory codec was troublesome for me, it made my Premier Elements 10 crash. So I went for the Lagarith Lossless Codec, but as I said it gives you HUUUGE files. It's almost 1 Gig per Minute. A 4m45 long video takes up 4.09GB.
What convinced me with Dxtory was it's ability to allow me to stream gameplay (to Twitch or Youtube Live) with it in addition to recording.
But you're maybe not interested in that extra functionality