Central Frankston and more particularly, the golden triangle is an excellent area. You are close to the central business district, uni, tafe, hospital etc. Obviously you don't want to back onto the train station, but other than that, look at street presence and go from there. But overall a great area
I just saw a guy peeing publicly. On Birdwood!!! Today!!! My 4 yo said to me: "Daddy, he's a weirdo, why doesn't he use a toilet?". I've been here over 10 years. You can probably do better. I would buy Frankston South or Langwarrin next time. But not Frankston.
Frankston central will be more profitable in the long run than langwarrin due to proximity to beach and amenities. Definitely prefer Frankston south, but both areas would be great investment choices. Perhaps get a feel for the different streets and work out which ones you prefer.
Every suburb has its issues. Visit the area your interested in at various time of the day and evening to grasp the overall vibe. But you could move into any area and have the neighbour from hell move in next door to you lol.