Cars.com has the most useful tool for comparing dimensions and other specs for multiple vehicles. Here's a link-
Just as an example, I chose the 2013 Ford Fusion SE, 2013 Honda Accord LX, 2013 Hyundai Sonata GLS and 2013 Nissan Altima 2.5S to compare. The Fusion has 44.3" of front leg room, the Accord has 42.5", the Sonata has 45.5" and the Altima has 45.0". So there's a variance of 3.0" of front legroom among these four vehicles.
Then I compared four compact sedans, the 2013 Ford Focus SE, Honda Civic LX, Nissan Sentra SV and Mazda3 i Touring. The front legroom is almost identical in these smaller sedans- a range of only 41.9" to 42.5".
With such close specs for front legroom, actually sitting in each model you're considering is the only way to determine which one is the best fit! There are numerous factors to consider- adjustability and comfort of the driver's seat, design of the center console and door panels and the position and adjustability of steering wheel and primary controls, to name a few.
When I bought my Mazda3 back in 2006, the Honda Civic actually had more front legroom space. BUT the parking brake handle in the Civic was positioned so that my right knee constantly rested against the end of the it- and it was not comfortable. I was also buying one with a manual transmission, so the position of the gear shifter and clutch pedal was also an important consideration. Being 6'2" and 225lbs, I can certainly understand the importance of having enough space in the driver's seat!