if you compare DC and AC..it's sure to have some difference between them...
Typically,AC give warmer tone than AC.if you looking for some sweety warm tone sound go for it but...HUM will come along with filament wiring.So ,plan carefully to avoid disturbance from AC HEATER wire...
DC give simply quite.. and very detailed sound... some people said it give too thin...
For series and paralell heater....I don't know about characteristics much but..if you can, paralell is better choice in my mind...When one tube is gone... another tube filament would not be heated too...
