An ISO is an exact copy of the contents of the disc, minus the encryption of course. This will preserve the structure of the DVD, and allow you access to all the items that can be seen in the menu.
Many people have chosen this format for their DVD rips in the past because it does play just like the original DVD. If you are using VLC for playback, then you should have no problem opening and playing the movies.
The problem with ISO files, as some people are now finding out, is the fact that many streaming media devices do not support them. If you intend to play straight from a smart TV, or through a streaming media box, then you should check their capabilities before purchase. Make sure that they can handle ISO files of DVD-video.