Power Transistor for TDA2030 audio amp
The answer can only be found be examining the TDA2030A datasheet, the TIP35C and 36C datasheets, and the circuit.  Since you didn't provide any links to these datasheets we can't tell.

However, "TIP" stands for "TI Power", and it looks like most any power transisors will work in those roles as long as the maximum voltage requirement is met.  Since you are apparently using a 48 V center tapped transformer, the power rails can be up to &plusmn;34V, so each transistor has to be able to withstand 70 V.

Again though, you have to check the datasheets carefully to make sure all parameters of the amplifier and transistors are met.  For example, the amplifier likely has some maximum output current capability, which may dictate some minimum gain for the transistors.  Also take the power dissipation into account.  These transistors will dissipate significant power, and will need to be properly heat sinked.

You say you are aiming for 25 W per channel, and your schematic shows 4 &Omega; speakers.  It only takes 10 V into 4 &Omega; for 25 W.  In case you may want to connect 8 &Omega; speakers some day, you still only need 14 V.  Since that is RMS, for a sine wave that is 20 V peak.  That would make the common voltage of 24 V per rail about right.

I would use a regulated &plusmn;24 V power supply (or two single-ended 24 V power supplies), not a transformer.  Modern power supplies usually cost less than the equivalent line-frequency transformer, but also produce nicely regulated output voltage with a wide range of possible input power line voltages.  Making your own power supply for something like this just doesn't make sense anymore.  The well regulated voltage allows you to get it close to the maximum peaks without having to leave room for droop, and then waste more power most of the time.