Need Advice on New Mower for Business

I have a few customers and I have currently been push mowing all my lawns with two 21 inch push mowers. It would be no big deal for me if it weren't for the commercial properties I have just added this year. The Lawn size on these properties is about 15,000 sq. ft. and it's is all split up around the parking lot. So it's not one big 15k sq ft patch of grass. I am looking at upgrading to a commercial mower just for the reliability. And the fact that I won't have to walk on two 15k sq. ft. properties any more. The gross lot sizes for my the rest of my residential customers is between 6,800-11,500 sq. ft. there is one anomaly though it is 14,500 sq. ft. but it doesn't take any longer because so much of the property is landscaped so even though that one seems bigger it really isn't :confused2:. The commercial property size I have given you of 15k sq ft is just the lawn size. But for the residential customers I have not measured their lawn size so I just got the gross lot size off of the internet I have not subtracted anything at all (house, driveway, sidewalks etc.) So my question is...what deck size would you recommend for these yard sizes? I'm am currently looking at a few stand-on mowers and walk behinds. I know a company in my town that uses 52-inch ZTRs for yards of this size but it seems like overkill to me. Also some of the lawn's backyards are fenced in but I'm ok with just taking a push mower back there if a bigger mower wouldn't fit. I'm just looking for any suggestions. I was leaning towards 36 or 48 but then I thought about a 52 because it really isn't that much bigger than a 48. But I like the thought of how easy it would be for a 36 to get around stuff in the lawn and in tight spaces. But a 48 would get the more open lawns done much faster.
Thanks,
Connor