I thought Charly may be able to point you to a good contractor. Send me your phone number, I may have a contact who can help with contacts, if not actual work.
Networking is key in this, it can be dog eat dog.
If you are on the road, then the weekly payout is better. You and your crew will have expenses. If you are local then you might be able to negotiate better contracts for longer payout periods. I've heard of setting them on specific dates so that the first payout is sooner then the normal calendar spread. Just to make sure that they do pay on time?
Go for the per tree, the per yard can bite you, since it is subject to how they load it. Yardage may pay if you are hauling debris yourself. That way you can get money form bot ends of the movement. The $25/tree you can budget better.
Being a bottom tier contractor is a chicken feed proposition. you need to do eight trees an hour to make $200/crew hour. Check to see what the work-hour requirements are. I've heard of primaries setting rules that did not allow any real OT, and since volume is how you make it on these operations...
The "working" contractor needs to get a clause for problem trees that do not fit the general model that sets the $25-per figure. If you can get it, just use it for the true PITA trees. This may lead you to getting other big problem trees that no one else wants on a T&M basis.
Most operations are circuses, you have to manage your crew time so that they are not spinning their wheels when the managing contractors are running in circles. You or a foreman may need to meet with management daily to get to streets you will be working, I've heard of lots of hours lost there. you do not want to crack the whip all the time, but i have heard of crews not taking the hustle seriously. Quotas and performance bonuses are very helpfull on these jobs.