I would be more than a little frustrated to have to choose one kind of diaper to wear for the rest of my life. There are times that thicker and solid tapes is good. Other times, thinner with Velcro is more appropriate. I tend to have more than one kind on hand. Not usually pull ups though.
Before making my choice, I would want to know more about how "kind" is defined in this instance. Limiting it to one brand, one diaper style (plastic backed with tapes?), or to one specific diaper product would change things significantly. The reason for making the choice would also be important. Is this for a lifetime supply free? Am I supposed to wear them all the time? Also, I would ask for a delay in making my final decision until after I could try some of the newer diapers. The Space one sounds interesting, the DC brand is coming out with a blue version, and Bambino has supposedly improved since I last tried them. Also would need to try the new NorthShoreCare and revised XPmedical A+ diapers (tried them on the first batch).
The style choice would be easy: plastic backed with dual tapes on each side. These are the best ones for high capacity and thickness at the current time. I like a diaper that works very well for its intended purpose. Wearing all the time would make Velcro or pull ups more convenient, but I need the high absorbency at night.
Limiting kind to a brand would currently make Bambino my top choice. A case of Biancos and Bellisimos each month would keep me happy. Add in an occasional mixed case and things would be awesome. The Biancos work reasonably well for wearing in public and those times when the thickest is not what I want and plain white is prefered. The Bellisimos work reasonably well for my overnight diaper; rarely would I want more capacity at night. A booster would solve that well enough. The coloring on the tape panel does not bother me at night. From past experience, I would want mediums for day use and larges for night/extended wear use. NorthShoreCare or XPmedical may be producing diapers which may work better for me, but I would have to test and see.
If kind means a specific diaper product, my choice would be Dry 24/7 in size medium. They have an awesome fit on me, really good absorbency, decent enough tapes, and have a good thickness which works both for public wear and private. The plain color white is my favorite diaper color even though my favorite color is black. This is the diaper I have worn almost exclusively since late last year and has been my favorite since they were color coded for size.
Abena L4s are a close second. For a time, they were what I exclusively ordered before Drys replaced them. My only issue is the fit is a little big on me and the capacity is a little lower than what I want. The mediums are way too small to comfortably fit me. Now that Drys are available cheaper by the case, I see no reason for me to wear these.
Not having tested some of the newer diapers, I cannot make the best informed decision right now. NorthShoreCare or XPmedical may be offering something better to me right now and I don't know it. This brings me to a final point: diaper selection changes every year and my needs may also change. The one that I would have chosen years ago is not what I would choose today. Next year may bring another favorite. My first favorite was green Depends, then I went to a mix of Tena and Attends, next came Molicare Super Plus, then Abena L4, with Dry 24/7 being my most recent favorite. Used to still buy Abena's L4 and L3 because they were cheaper until Drys became basically just as affordable. Now, I would want to confirm my choice before making a permanent choice. So glad I can buy and wear more than one kind.