Depends on types of fields you have, if you have help at harvest, also do you have to road travel on busy highways much, also what size planter are you using and how good are your guess rows between passes. 

 On shorter rows or smaller fields a larger head would be nicer since you won't need to worry about folding the ladder up every time you get in and out.

You also need to take into account which tires and spacing you have on the rims. My Hi Tin 443 on my 6620 T2 was a tight fit to the next  row with 24.5x32 tires. In soft ground or leaning corn or on pinch rows between planter passes (if say planting 6 and shelling 4) it can be an issue.

With a 6 row in longer fields you may not be able to make full rounds. I have that now where I can make about 75% of a round then have to run to truck to dump. I alternate passes instead of working lands trying to stomp rows in the direction they will be planted the following year. I'll make several rounds this way then go back and clean up several of the unfinished short sections all at once. That sort of throws off my stomping pattern a bit but has not been an issue yet.  I work alone so maximum efficiency and capacity to keep combine moving is not a consideration. Shell enough to load truck, stop, haul to elevator, come back go again. I like working alone and not having to crowd everything all the time.

If you have longer fields and no help maybe being able to make full rounds would be more beneficial. Personal preference to what works for you.

Hi Tin vs Low Tin I would give the thumbs up to low tin, those high end dividers can be problematic in down or broken over corn due to wildlife. A further plus is plastic snoots for these conditions as they are much more slippery and with built in ear savers don't impede the flow. The sheet metal ear saver extensions are a real impediment in down or leaning corn. Oil bath drives on later ones are maybe somewhat better but the old dry drives never gave me any troubles.

I converted my old 443 to knife rolls and updated triple gears. They would not allow much on a trade when I went to the 693 so that does not really add much value to the smaller heads. I decided to keep it and have the Roll-A-Cones mounted on it so it sits in the barn as my emergency rescue/backup head.

Take a good look at tin work, stalk rolls, auger, sprocket teeth to gauge wear, also look closely at upper gathering chain sprockets for wear and make sure that shaft coming out of the gearbox is tight. They run in bushings that are fed grease from the gearbox via a spring on the internal shaft that feeds grease up to that bushing. If the boxes have been ran with out checking and/or adding grease this bushing can be starved of lubrication leading to wear.

Just a few of my observations others will have more and your mileage may vary.