For me, I set me budget and then looked at what I could get within that budget. You definitely want a thumb on that machine, so factor that in, if you buy a machine without one, depending on size that is a minimum of $2500 to get a thumb and even more money if you have to pay someone to weld it on. Ideally, you want a hydraulic thumb. Mine is manual, but it has an extra valve in the main block to plumb an extra hydro cylinder.
I ended up with a 120 size machine because it fit my budget better and had a thumb, the 200 machine did not have a thumb, so between transportation costs and the cost of the thumb, my 120 was $4500 less expensive than the 200, and less operating and maint costs.... It will also me cheaper to move should I decide to do some lot clearing for some extra money.