It depends on how much I am likely to be feeding.
On my local club lake, opposite the front door
there are so many little rudd fry in the top layer of the water that an entire slice of Sainsbury's cheap 47p white sliced Basic loaf can go from being chucked in to no longer existing in as little as 45 seconds. I've timed it ! In such conditions I can easily get through feeding 5 or 6 loaves in a four hour session.
Nothing fancy, just a whole slice or three at a time frisbee'd in with the best accuracy I can manage. With just a couple of slices on top of lilly pads... damn good fun watching a big old carp nose whiffling away below and the crash 'n dash as they turn the pads over.
For hook bait I tend to use either a slightly better quality Warburtons white or, if I am feeling flush, a big fresh crusty tin loaf. Ball up the soft inner bread to golf ball - Cricket ball size, and / or use the crust as a decent hookholding surface floater.
Again, big pieces.
Learnt my lesson with small pieces - remember them Ruddy (see what I did there ?) fry. A Cricket ball size lump may seem huge but believe me a respectable carp will swallow that down no probs if it wants it, and with the little fry dashing in and tearing at it it doesn't stay that size very long either.
In passing, cricket ball sized lump of soft crust has always been my best big Bream bait as well.