If I'm not too late to chime in...
Reading this post there have been a lot of good good points pro and con to both types of mowers. For what it's worth here is my two cents. I was originally a true blue long time user of Walkers. Over the past four years or so I have been investing in the Toro Grandstands with mulching decks and getting away from bagging everything. The Toros have been excellent. Very comfortable to operate and my back does appreciate it over a rider. They also have been able to handle most hills. Not as fast as a Lazer but definitely faster then a GHS Walker even with a speed up kit. But here are the cons of the Toro Grandstand or any other stander. They are tougher to sharpen blades, clean the undersides of the decks, and have a bit of a steep learning curve especially if you have employees. But still definitely a nice machine. However I found myself migrating back to Walker for their Super B with a 52" rear discharge/mulching deck and also their new MB 23EFI with a 48'' mulching deck. I did this mainly for their speed and cut quality. Both of these newer Walker machines are totally different than the older GHS units. Cheaper, faster, and have a simpler design. They also handle hills better than any other machine I have ever used in my 26 years in the biz. Combine their performance, ease of servicing, and ability to use different deck and implements they are a great option to consider. Definitely something you should demo. As to bag or not to bag... We have been solely mulching for over four years now after bagging for 22 years and we have not yet received any complaints. You just have to re-train yourself and your employees on how to properly use mulching mowers...there is a difference! Mulching decks have come a long way in recent years and are worth considering. Our yards have been healthier since we switched to mulching. But more to the point of the original poster's concern. Since you were originally a Walker user I think you would enjoy the Walker MB or Super B over a standing type of mower.