If you're trying to stay under 20K, then a 3 is a no brainer and you could get into a 5 as well. Honestly, I wouldn't own a dozer smaller than a 3, which this 550 is. And if I really had my choice, I wouldn't own anything less than a 5. The footprint difference between a 3 and 5 is moot and you gain ponies and weight. Don't be afraid of a C series Cat or a G series Deere, they may be older but they're almost as productive as the new gear.
Go hard, go fast, or go home