Are you thinking there will be any more machines in your future? If you are intending to get more machines, are you thinking of purchasing new?
Industrial machines from about the 1950's forward are very nice and widely available (at least in some places) - they are nearly always 3 phase and will often have multiple motors.
If you are purchasing new you will often get to choose single phase or three phase (same as what you are doing now). Of course what ever you finally choose, no reason you can't go down the other path at a later date.
I have about 9 (?) three phase machines connected and running (probably 15 different 3 phase motors) - I don't think it would be practical to run them on some sort of a VFD system. I have one drill press (3 phase) running on a single phase supplied VFD (it worked out easier in my shop arrangement and how the power was set up originally).
I am running all the machines off a 5HP rotary phase converter (my largest motor is 5 HP). It works awesome - I can just keep on plugging in more machines. It is true that the rotary units make a "fake" 3 phase power, but it works great and I have never had a problem.
There is a more deluxe option which has not been mentioned - using a Phase Perfect to get 3 phase power from a single phase source. Again, you can just keep on plugging in more machines to the capability of the unit. With a PP, the power quality is excellent - generally better than grid 3 phase as the voltage control is managed on site and not subject to the vagaries of the distribution system.
The VFD option is a good solution, but it is not "plug and play".
It really comes down to what you want to do with your machining. If you only plan to get the one machine (and with just a lathe and the usual small machines and work space + tools, you can have a very nice & capable shop). Lots and lots of iron really is not necessary to do much good work.
Single phase or 3 phase are both good options. If you are just doing an opinion poll - I'll put in my vote for 3 phase.
David