Grigore,
Toroidal transformers have some significant advantages, specifically, their EMI fields (which can introduce hum into circuitry) are limited and what does exist tends to be perpendicular to the torus, and they are efficient in terms of bulk and cost. But as generally available, their disadvantage is that they have extremely wide bandwidth, and whatever noise enters the primary, exits the secondary(s). If the toroids that are available to you are custom built, you should inquire as to whether they can provide a grounded electrostatic shield between primary and secondary. This provides a capacitive shunt for noise and makes the toroid and excellent choice. If your source is actually going to wind your transformer on spec, the addition of such a shield should be of minimal cost.
Other types of transformers, EI core when properly implemented, double 'LL' core, R-cores 'C' and double 'C' core are actually preferable to the typical toroid, save for those first two mentioned advantages. But they are usually far more expensive than toroids in the sizes required by amplifiers.
To whatever extent you believe power line noise is a problem, besides an internal shield, you can implement power line conditioning external to the transformer. Toroids, whether shielded or not, also have the advantage that rectifier noise is minimized due to their low leakage inductance.
Regards,
Paul
