I will be the odd man out and vote for the 6620. We have always ran deere combines and also had a 410 massey for a while. Compared to that massey the deeres in my opinion are easy to work on. The only thing I know of to watch on an older used deere combine is the auger pan under the concave and above the transmission. If it is an outside machine and wasnt cleaned out after each harvest these pans can rust out and can be tough to patch up. I bought my 7700 four years ago for $1500, it now has over 4500 hours and I havent done any work at all in the last four seasons, other than change oil and a few chains. The 20 series have the bearings mounted away from the machine so if they do need replacing they are easier to work on than the 00 series. I don't know much about the IH's, but I have heard of them breaking axles, but I do think they have more capacity in crops like corn.