Minolta was the first company to introduce a viable AF SLR and was one of the largest camera manufacturers, Sony purchased all the IP when it took over the company. A lot of the Sony lenses are updated Minolta designs, so they have a good pedigree. The Carl Zeiss Sony range is excellent if you can afford it, you can also use a lot of the Minolta AF lenses, which is quite a big range.
This is from the DPReview review of the SLT A55, sometimes AF in video has it's own issues.
"But, because of the shallow depth-of-field offered by large sensor cameras (and depending on the subject) shooting video with AF might not be entirely advisable. Firstly the camera doesn't always focus on the subject you want it to focus on which can lead to visually unpleasant 'focus jumps' and secondly the noise of the focus motor can be heard on the audio track. Although the latter can be avoided by using an external microphone, due to the narrow depth-of-field of an APS-C sensor camera such as the Sony SLT-A55, even small shifts in focus will be much more visible than on small-sensor camcorders or compact cameras."