To me at least, Rosebud sounds feel the best.. The bulbous tip on them feels amazing as it slides through and when it penetrates the opening of the bladder, intense in a good way...
make sure they are sterile.. A good set can picked up for under 50-60..
Only use sterile water based lube like KY or you will get/give an infection.
Start small and don't progress to larger than is comfortable..
For added pleasure, you can add stim from a TENS, or EMS easily by attaching an adhesive electrode to the handle end and the other adhesive electrode to the scrotum or taint region (I prefer taint)..