The higher transmission rate will provide a higher quality image on your phone or tablet. But, as you get farther away and the signal gets weaker, you can wind up with jerky, glitchy images. The lower rate will reduce the occurrence.
If you're using a mini tablet or phone, your best bet would be the lower rate since you're viewing video on a small screen. The lower rate will have no affect on what you record to the SD card. But, if you cache video on your tablet or phone it might reduce the quality of the video. I'm not sure about that. I never cache video to my device.