I've seen a presentation by the Mr. Landlord guy. Seemed very knowledgeable and appeared to have some reasonable systems in place, especially for lower-income tenants and larger muti-family units.
Don't know how much he charges, so I can't comment on the value, but he does seem legitimate and experienced.
I settled for 123Landlord.com. The thing that I found clunky with the rest of them was: You need Work orders and track what gets paid for what property and what tenant, expenses bills and so on. Open work orders, in-progress orders, advances made to contractors. yes this last one is BIG, you always pay 50% down say and the rest on delivery. I couldn't find a system that was handling all this stuff so nice. Plus the price to start with few units is two Starbucks per month :)