Best bet is ask the dealer why they chose the brands they did, how long they've had them, who wholesales them locally. Neither brand is well known but both are above average in quality from what we see of the industry. We feel that is more important than name recognition. It helps to stay with the same brand so your techs get to know it. That doesn't do you any good.
Most existing equipment is too large.
But big furnaces cycling constantly are not efficient nor do they deliver even comfort. Big air conditioners cycling constantly aren't efficient, they don't remove moisture well nor do they cool evenly. The newer high SEER units are particularly bad at moisture removal in the first 7-8 minutes of operation. The only way to know is survey the house. Then use a spreadsheet to determine exactly what size you need.