CCA is a measure of starting power at 32 degrees (which is not an issue in Louisiana) but is also an indication of overall starting power. Higher CCA batteries are apt to last longer and be better at starting. Overall, I recommend you get the highest CCA available at a reasonable price.
Riding mowers today can typically use 230 CCA batteries and 300 CCA batteries are found in larger engines. Cost may be the only difference you see but I can't say whether it's OK for your mower. It may help to know the temperature range you use your mower.