I have always been told highest grade you can afford of the lowest mintage you can afford. Gold and silver fluctuate with the market, but numismatics tend to be driven by market and mintage. If anyone here can predict the market otherwise I am all ears. However, a smart investor might keep that magic formula to themselves.
For dealers it can be dependent on product placement. who comes into there shops or how many views they get on an auction site. I have one dealer friend who can sell through a roll of Kennedy's in a week without trying, and another who struggles to recoup his cost on the same rolls. However, the second dealer's clients are most interested in classics.
Unless the grade is of particular historical and collectable significance, low ball ancient coins are in the eye of the beholder. I have seen a lot of general ancient sales based solely off family lineage or historical buffs.
I collect for my own passions. I love the artistry of it all. Some collectors hate on the
Peace dollars, but I personally think it is just a beautiful display of art form the 1920s (Here come the Morgan lover comments :) )
As it has been said a billion times on CFF. Collect what you love. There is a lot to consider when looking at coins as an investment, and most often one should not expect an immediate return. Like most investments worth making, you are not going to buy a silver dollar one day and sell for 400% profit the next.
I find building the relationships and community around collecting a far better investment strategy.