Without getting into the "which is better debate, Houses, Townhouses, Villas or Units??", I preferr to purchase Townhouses & Villas with a 30% or greater land component (thereby eliminating multi story units or high rise apartments), for several reasons.
The mains ones being (in no particular order) -
1/ lower maintenance & upkeep for the tenant
2/ lower purchase or entry level into a Higher capital growth suburb area
3/ rapidly growing marketplace (starting both now & into the future) wanting these type properties. This is due the largest group of people to ever be born (being the Babyboomers and Empty nesters) starting to come into their retirement years.
They will be wanting to downsize for lifestyle & economic reasons.
4/ greater tax advantages & tax effectiveness thus maximises cashflow.
5/ able to hold more individual properties spread across your portfolio - thereby minimising area over exposure risks by not holding all your eggs in only a few baskets, so to speak.
Hope this helps.