Trouble With Two External Drives?

I have two external drives (Seagate 2TB and Western Digital 1TB). Had the Seagate since August and purchased the Western Digital because I was having issues with the Seagate. I have a ton of photos on the seagate.

When I connect the Seagate drive, I have like a 75 percent accuracy with it working which is why I purchased the Western Digital drive. When I connect the Western Digital drive, it works MUCH better. However at times, the Western Digital drive does the same thing as the Seagate. Both drives will show up in disk utility, but one will be greyed out and the other not. The seagate works and the western digital won't one time and the same happens but the opposite another time.

Both drives are formatted as EXFAT so I can read and write files of ANY size. I am running the latest version of yosemite. Any help is appreciated!!!