First of all, HDV stands for High Definition Video, while AVCHD stands for Advanced Video Coding High Definition. HDV is a tape-based format, which was earlier in used for HD quality video recording. Conversely, AVCHD is a later version, which offers tapeless formats for storing videos.
It is more portable and convenient to use, even as it generally tends to be smaller than HDV devices, it is still cheaper. The AVCHD format makes use of the newer MPEG 4/H.264 specification, while the HDV makes use of the older and later MPEG 2/H.262 specification.
HDV camcorder is fixed at 25mbps, whereas AVCHD camcorders usually have a bit rate of 17mbps or 13mbps, or even lower. AVCHD camcorder provides an advantage whereby you can easily retrieve your videos in order to save them on the computer. While HDV lacks the ability to burn directly to Blu-ray, AVCHD is of an advantage here.