May folks have found that the Ulead line of programs work extremely well. As to "converting" VOB to MPEG. It already is MPEG, you can simply re-name the files. However, most DVD-video is broken into 1 GB files so it's better to use a program that will import the entire DVD (whether it's on disc or on the HD in a folder). Any decent authoring tool will import an entire DVD.
If you wish to have one big MPEG file to work with, just use DVDShrink to rip the DVD, with Shrink set to create one VOB instead of breaking it into 1 GB chunks. Then just re-name the VOB to MPG, and you're set to re-author. If you already have DVD-video, and you simply want to re-author with minimal editing, you can use most anything for that. It really depends on how much editing you need to do, and what type of editing.
Suggest you download a free trial of Ulead DVD Movie Factory and check it out. If you need a more robust editor, Ulead VidioStudio 10+ would be the choice. If all you need is a simple authoring program with limited editing capability, suggest TMPGEnc-Author 1.6.