I wouldn't bother with void until you get good at prayer/weapon switching. Afterwards though it's definetly the best. Although it doesn't take much to get used to, but yes probably not best for using straight away.
If they have the skills a lot of the time levels don't make much of a difference. They still help but being able to tank well is more useful than just having high def/prayer and not being able to tank.
So today I went and defended the mugger, and got a MASSIVE 2k defence exp for my job well done. 92 farming on the weekend, and hopefully some mining levels.