One reason that a shower would leak even after replacing the Delta cartridge could be because of the O rings. You may have to replace them.
Did you replace /check the seats also?
You twist the knob.
pull it or twist it
The ball very seldom is the problem it is the springs and cap washers
Delta is one of the leading faucet makers and their products are known for their exceptional quality. Their major competitors are Braun and Moen. Check out amazon.com and epinions.com for reviews.
If the water pressure is fine in the rest of your house. The supply pipes are either too small for how many fixtures they serve/the shower's distance from the main. However, more than likely you have galvanized pipes that are corroded and they need to be replaced with copper or pex.
Defective divertor
Some popular shower massage heads include the Oxygenics PowerMassage and the WaterPik PowerSpray. Other popular brands include Delta, Pulse, Vigo and Moen.
Moen and Delta shower controls are similar. Either one can be fitted in same locations. Both have versions for soldered pipes, threaded fittings , or PEX fittings. Both companies make a huge range of controls, so there is something to suit everyone.
The website "Steamsaunabath" has how to guides on building and choosing the proper components for a steam shower bath. Get advice from professionals at plumbing shops like Kohler and Delta.
You need to buy the extractor tool from Home Depot.
There are many companies that manufacture shower taps. Among these companies are Delta Faucet, Peerless Faucet, Moen Faucets, Kohler, and American Standard brand faucets.