To me the best squishy and really absorbent diaper would be Abuniverse Super Dry Kids diapers which is a pampers replica of the old plastic backed pampers diapers.
Abu Kiddo Diapers are also very squishy and swell up nicely.
Northshore diapers such as the Northshore Mega Max adult diaper are also really absorbent and squishy diapers.
When it comes to squishy diapers the baby diapers such as Pampers Baby Dry or Pampers Cruisers, Huggies, Luvs etc are all really squishy because those higher end diapers contain SAP and not just wood pulp.
Some cheaper adult diapers contain mostly wood pulp in them which is not really squishy or great to masturbate in.
Some squishy adult diapers though that have a lot of SAP are Abuniverse diapers such as ABU Super Dry Kids diapers which is a pampers replica.
Or Bambino diapers.
Northshore supreme diapers also have a lot of sap and are really absorbent and squishy.
If you have current adult diaper that are not very squishy you can stick a baby disposable diaper in the adult diaper and wet it.
Then that baby diaper will be good for masturbating your penis against if you're a guy.
I'm a male and I also love to masturbate in wet diapers.
I've tried the masturbating through use of the hand and some lube but I find it much more pleasurable to put a disposable adult diaper on and then wet the diaper.
Once the diaper gets wet with pee I get turned on and my penis gets erect and I start rocking my body back and forth sitting on a chair and will move my penis up and down in the diaper.
The penis rubbing against the wet sap in the diaper makes me explode into the diaper with my semen.
Actually I'm masturbating in my wet adult diaper right now sitting at my computer.
I love masturbating in diapers because you don't need your hands or anything to clean the semen up.
The best adult diapers to masturbate in are those Adult Baby diapers such as Abuniverse Super Dry kids or other diapers from them.
Tykables and Bambino diapers are also great for masturbation.
I also love to place a Pampers diaper such as Pampers Cruisers size 7 diaper on using some packing tape and wet that diaper.
The SAP in the Pampers Diaper is so great and it swells up nicely and feels really great against my penis.