Faced with almost the exact dilemma, I chose the BX and BOY am I GLAD that's how I went. I mow a little more than 1 acre of heavily wooded grass and can get it done (including bagging) in about 45 minutes (that's tractor time...not trimming and such).
1* Perhaps I could get that down to 30 or even 20 minutes with a ZTR, but along with gaining 15 to 25 minutes of my life, I'd lose one of the best tools I've ever purchased. I do EVERYTHING with my BX and the mow quality is exceptional.
Alternately, my cousin mows 5 acres of open field every week. That's his yard. His Kubota ZD21 FLIES and gets the job done much faster than a BX would. In his case, he's much better with a ZTR and a non-mowing
B21...the exact solution he's deployed.
If you're looking for one solution, go with the BX. I hate renting things. Don't like the timetable it puts on my projects.
2*You'll gain little time in mow speed and give up HUGE amounts of utility.
To give you an idea of how quickly a BX could dispatch 10 yards of mulch: I trailered my BX to my parents house (~3 hours away) to help fix their 1/2 acre yard. After I completely re-graded their ditchline and cut/filled numerous places in their yard (as much as 1 foot in places), I spread 6 CY of screened topsoil and 6 CY of compost blend. I evenly spread and graded that 12 CY of material in about 1 hour. I completed the entire lawn rehab job (including many, many other tasks) in 1 day. The next day, my Mom asked me to get the roots out of the back yard. Using the backhoe, I pulled ~1,000# of roots out of the ground and regraded the back yard for grass planting...that distraction took about 5 hours start to finish.
The BX is wicked-amazing.
