Quality Lifts
There are only two brands of lift that I would put on my rig, Skyjacker and D1ck Cepek. There are many other companies out there, some of which do indeed make quality lifts but as far as our Rams are concerned nothing can touch the above mentioned.
I had the SJ 2. 5" coils on mine and it leveled the truck out perfectly and improved the ride quite a bit.
I now have the SJ 4. 5" kit and absolutely love it. I haven't had to touch it since the install. A very nice quality lift that comes with everything you need to do the job.
If you decide you want a little more lift I recommend the D1ck Cepek Extreme 6", very nice set up. Or the Skyjacker 7".
As for pros/cons the only thing I can think of is the dual shock set up on the SJ system. A lot of guys run it with no problems but I personally don't like the set up. If you want dual front shocks I recommend looking at Fabtech's set up.
Some of the others use spacers on the front coils which will get you by cheaper but personally I like the improved ride with the new springs. If you look at lifts other than these be sure that they have the correct coils to support the Cummins. I talked to several dealers that said they would work but they were the same springs they used for the gassers.

Stay away from Superlift, I have seen problems with these lifts first hand and their add states
"Note: lift height will vary slightly depending primarily on whether your truck has a gas engine or the heavier diesel engine. " They say that because they use the same springs for both unlike Skyjacker. I know guys running the Superlift that didn't get the advertised amount. I actually got a little extra lift with mine and SJ guarantees the coils not to sag. If they do, they will replace them but I haven't seen a case where that happened yet.
The post above pretty much sums up the flex issue. If you're not into rock crawling you don't need either of the flex options. You'll be fine with the basic kit. I got mine for $900, the flex isn't worth the extra $$ to me because I don't crawl with it.