Portables have made a huge leap forward by increasing CFM and higher quality components / pressure pumps.
Choose a portable that will fit your service menu.....meaning if your going to offer "tile & grout" cleaning along with carpet and upholstery then make sure to buy a portable that has adjustable pressure from 100-1000psi
And since the pump it the heart of the portable make sure it has a "high quality" pump and vac motor.
Without a doubt after you work with a portable any length of time you WILL want to purchase a truckmount.....faster set up.....better dry times....high heat for greasy jobs ect. However, if all of your work is going to be commercial high rises then a portable is the best option.
Check out the " New & Improved"
Sapphire Scientific "Versaclean Portable" line.
Full range of portables to choose from 200 with or wo/ heat up to adjustable " high pressure " for tile & grout cleaning with the best high pressure pump on the market using a " General Emporior" pressure washer pump and 6.6 Ametec vac motor with 140 CFM. See the line up at
www.sapphirescientific.com and look under "Extractors"