I had the same debate. Starting out with a 68 C-4 setup.
I thought for 1 year that I'd do the t5, but am doing with the AOD.
Gathering the clutch parts and brake parts just seems too much. And I'm happy (so far) with the AOD install.
Now I haven't driven it yet, but hey, I'm getting there.
Your specific questions:
I think the cost is better AOD (because youre starting with a C4)
I think it will be easier. They have all the parts now (that you need to convert)
And, the transmission just goes in. All you really do is fabricate new cooling lines.
As someone with a T5, I would have to agree that an AOD is the way to go. The linkage is just a pain, at least on a 70. For the last 18 months I've had all kinds of trouble with various cable linkage setups. Currently, I get about 20 minutes of driving and then the linkage starts going out of adjustment, leading to the ultimate frustration of sitting on the side of the road trying to muscle the car into 2nd in order to limp it home. Hence, I vote for the AOD. On the other hand, if you are decied in your opinion that you have to have a T5, then I recommend going with a hydraulic clutch linkage setup. Once installed it never needs adjusting. JUst my 2 cents worth.
I'm sure an AOD is easier and cheaper since you already have an automatic. I went through the same debate though and decided on a Tremec 3550.
I was trying to decide between an AOD, a Gear Vendors overdrive and a 5 speed.
I discounted the Gear Vendors because it didn't have as high of a final overdrive as either the AOD or the 5 speed. It also seemed somewhat like a hack, although the people that have them seem to like it.
I didn't go with the AOD either. Two years ago when I was researching, many people had issues with the strength of an AOD and with the TV linkage. They were also more expensive than a 5 speed (more on this though).
I chose the Tremec 3550 over the T5 because of the extra strength. I have driven manuals mostly so having to shift didn't bother me. The 5 speed also meant SWMBO couldn't drive it, which was fine with me and her. It seemed to me I would have less problems in the future going to a 5 speed. I have not had problems but some would say clutches and the acuation system can be as much of a problem as anything on an automatic. I'm using a hydraulic acuation system and a Centerforce II clutch and it has had no problems. It was more difficult rounding up all the parts to switch from an auto to a manual and I'm sure it ended up costing more than an AOD swap because of all the extra parts.
One thing I've been meaning to add to that page is the swap would be quite a bit easier if you bought an aftermarket cable shifter rather than convert a stock shifter to operate a cable, as you'll see I did. HOWEVER, I don't think you can use the aftermarket shifter AND a stock console without some SERIOUS modifications. In other words, if your car doesn't have a console, and you don't mind putting in a B&M Hammer shifter (very cool), a 4r70W swap would be simpler.
I also installed an AOD to run behind my stroker.
Because my motor would rip a standard AOD to shred I bought an AODDominator which gives all the gearing advantages of an AODE and is built bulletproof for up to 700 hp and ft lbs....off course at $2,000 not counting the install parts it might be more than most need but it was still cheaper than buying a new tremec and collecting all the other install parts to convert to a manual.
say hoosierbuddy, what did it run you for a grand total for your 98 V-6 mustang tranny install? checked out you website and you did a great job installing that. looked like alot of extra parts that may run up the bill for all the electronics stuff. interested in repeating your tranny install on a 70 but i am curious on the price comparison.