best software for real estate investment

Excel always has a welcoming smile and an easy-breezy outlook.

Or do you mean small landlord type software?

By which I mean you might want to clarify whether you're trying to come up with a buy/no buy (or purchase price) decision, or are you looking for something to help you manage the properties on an ongoing basis (lease expirations, accounts, notices, etc.)?

any game software that occupies your time so you forget to buy the building.

argus

Argus seems very grownup. I'm assuming OP is asking about small-scale landlording. What are the best options for 4-50 units. I've seen online things, even free ones, even cloud-computing ones ... I'd be very worried about migrating the data to something else if it becomes necessary, or even simply desirable. I imagine it's all proprietary, but maybe just built on a popular database.

something to help manage my property and
helps me choose the best investment property, calculates market cap rate
something you plug in numbers and it gets you all the important results
something that will in turn convince other investors to join in etc....