Would a suprapubic cathether be better than ileal conduit surgery for my of aged dad, with bladder ca?

Depends: Does he need his bladder removed for the cancer? If he does then it's a mute point. Sometimes they divert to stop bleeding.

Not likely: Suprapubic catheters are not a good choice in bladder cancer as it can potentially allow spread of cancer outside the bladder via the suprapubic tube tract. That said, ileal conduit construction is major surgery. A Foley catheter would be a better choice than a suprapubic tube if no other options are feasible.