As already stated by Bob_Skurka, definitely get a "3-way" blade. I've always called the movements on this type of blade tilt, angle, and offset. Also make sure you can swivel the blade 180 degrees while on the tractor and that even in the reversed position you can set various left/right angles and adjust the offset.
Some other things to look for on a blade would be a reversible cutting edge for long life, removable skid shoes, removable end plates for pseudo box blade capabilities, a hydraulically adjustable gauge wheel option, the option to have all hydraulic adjustments for tilt, angle, and offset, and finally, weight. Lots and lots of weight! Another thing you need to consider for a rear blade is its width. You want to make sure it is wide enough to cover your rear wheels even when set at a reasonable (30 degree) angle.
Finally, all rear blades have some kind of "maximum horse power" rating. Be sure to find out if that specification is for gross engine HP or PTO HP. Also note that most manufactures will de-rate that HP rating for 4WD or MFWD tractors since they generally have a lot more traction do a lot more pulling than a 2WD tractor.
I've been using an 8' Servis "Little Rhino" blade for 33 years on my current 2WD JD 1020 tractor. It has been a very good blade The equivalent blade today is known as the Rhino 500. The one possible issue with Rhino blades is that they use proprietary bent pins to index all their movements. The only pin that has ever been an issue for me is the pin that sets the blade tilt. It has been prone to falling out, but it was also the only pin that was tethered to the blade frame with a short piece of very small chain from the factory. This prevented the pin from being lost.
I know you just got your JD 4720, which is also one of the tractors I've been considering to replace my current JD 1020. The rear blade I've been coveting lately for a 4720 is the Rhino 950. Why? It is the heaviest blade I've found that still has CAT 1 hookups (actually it has hookups for both CAT 1 and 2). It is also available with the aforementioned optional skid shoes, quick attach end plates, full three way hydraulic adjustments for tilt, angle, and offset, as well as the ability to add a hydraulic gauge wheel.
Here's and image (linked off the Rhino website) of the Rhino 950 with hydraulic adjustments for tilt, angle, and offset as well as the optional skid shoes:
Here's and image (also linked off the Rhino website) for the optional end plates as shown on a Rhino 800 blade (same as the 950):
And finally, here's an image for Rhino's hydraulic dual gauge wheel as shone on their 1540 blade (step up from the 950). I don't know if the gauge wheel on the 950 is a single or dual wheel setup:
I know that in one of my posts to either one of your other threads or a thread you were participating in that was discussing the number of hydraulic services to have on a tractor, I had thrown out my "rediculous" requirement for a total of 8 services (3 for FEL and attachment, 2 for Top & Tilt, and 3 rear). As you can see, my ideal Rhino 950 setup requires 4 of them! However, I had planned to use the manual tilt adjustment on the blade for gross tilt adjustments and use the Tilt on the Top & Tilt to make subtle tilt adjustments to the blade. The gross tilt adjustments on a blade are too course for crowning work which must be done by adjusting the draft links on the 3PH.
Any way, could you "get by" with all manual adjustments on a rear blade? Sure. I've done it for 33 years. Is it a pain? Absolutely! To the point that you tend not to make the subtle adjustments you really need to for a top notch job. I absolutely long for the day when I'll be able to make all the adjustments on a rear blade (or even a box blade with the Top & Tilt) from the tractor seat on the run. Now that's some fine living! /forums/images/graemlins/grin.gif
By the way, that hydraulic gauge wheel option is something I learned of only recently. Although I've seen manual versions of this, the hydraulic option actually makes it look useful and it looks like just the ticket for creating smooth roads or removing "whoop-de-doos" from existing roads. The gauge wheel option, at least as Rhino implemented it, turns a rear blade into "float" implement. In combination with the side plates, it should work wonders in smoothing out fields or roads or pad sights or whatever.
Next to the FEL, a fully optioned out Rhino 950 rear blade would be my second most used implement. Building and maintaining roads, ditching, smoothing, leveling, snow removal. Not to mention some serious counter weight ballast for the FEL!
And no, the Rhino 950 outfitted with all the options is not going to be a "cheap" solution. Especially when you add in the costs of getting all the hydraulic SCVs on the tractor needed to control it. But then again, this is one of those "you get what you pay for" solutions. Hey, we only go around once, right? /forums/images/graemlins/grin.gif