not an expert on the subject, but I've run into the same decisions myself... The 700r4 has a very short 1st gear, so it's nice for a little extra boost off the line, but the 1-2 shift can often seem extended. They are also not ment to handle any power, so a shift kit and rebuild is highly recommended.
the 2004r has more evenly distributed gears. 1st is also a little larger, so it's nicer for naturally torquier cars. I don't know what the overdrive ratio is, but it's roughly similar to the 700r4. They were build to handle a little more power than the 700r4, but rebuilds and kits are still recommended.
running a high rear gear like 4:11 on a 700r4 will make 1st gear seem TOO short, where the 2004r will seem nicer.
the 700r4 is 3" longer than the stock setup in a Gbody. So the driveshaft will need to be shortened and the crossmember will need slight modification. The 200r4 requires no modification, I believe, and I believe it is the same length as a th350.
I am using a 700r4, but from my research a 2004r seems a better choice for my mild 355 with 3.42 rear gears.
I hope this helps...