Well....your questions is rather vague.....
But in my humble opinion...I would go for Carrum Downs....why???
Too many people jumped on the Frankston bandwagon....Carrum Downs does have a lot of infrastructure and is reasonably priced. Frankston still has potential but more competition for stock...
My mate bought a brand new villa (it is on a 300 sqm block of land with a backyard...so more like a house) off the plan in Jan. 2008. He settled in May 2009 and put a tenant for $280pw. He paid $259K.....it is now worth about 320k!....and to top it off he paid less than $1k in stamp duty...plus he gets depreciation allowances.