WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
Building, troubleshooting and testing of these amplifiers should only be
performed by someone who is thoroughly familiar with
the safety precautions around high voltages.
I have used 45 and 801A output valves (the latter being higher-rated 10 types) and found the 801A best for Lowther/Lowther-type speakers. I believe it is due in no small part to the higher impedance driving the intrinsically highly damped drive units.
I also find the "thoriated-tungsten sound" more subtle than the more prosaic 45.
However, I do believe the two types of valve to be the very best for playing music through efficient speakers and final results will depend on the driving valve(s) used, output transformer and power supply.
To these type of question you will always get different opinions. It is the entire amp and especially the driver stage which determines the overall sound.
I have used 45 and 801 with the exact same driver stage and similar power supply which allows a better comparison. Still the output transformers play a role which have to be different for both tubes. Also the 45 can be AC heated while you need DC on the 10Y if you want low hum. The DC filament supply will also have a large impact on the result.
In my comparisons the 801A (uprated version of 10Y) is more detailed, has the better solution. But if would call the 45 more refined.