The loudest will be the one with the highest sensitivity spec. So, if #1 has a sensitivity of 103 dB SPL/milliwatt and the #2 has 113 dB SPL/miliwatt, then #2 will produce a louder sound at the same input level.
HOWEVER, the marketing dweebs at the headphone mfrs are not going to make it that easy for you...
For example, let's take a look at your list. From their respective web sites:
First, the Yamaha EPH-100
Sound Pressure Level 104 dB ±3 dB
Umm, OK - what the heck does that spec have to do with the sensitivity? We don't know what the input power was to achieve that 104 dB level. 1 milliwatt? 1 volt? 10 volts?? And, what does the +/- 3 dB mean? Over what frequency range?
The Yamaha spec is COMPLETELY MEANINGLESS!!
OK, let's try the Philips S1
Sensitivity 107 dB
Well, at least they called it "Sensitivity". But still, we have no idea whether that is for 1 milliwatt, 1 volt or 16 bananas.
The Philips spec is COMPLETELY MEANINGLESS!!
Strike two!! Should we try for 3?
C'mon JVC FXT90!!
Sensitivity 107 dB/1 mW
Ding! Ding! Ding! We have a winner!! This spec actually means something!!
OK - now I'm curious, do we quit now or go for a double?
We should have quit while we were ahead...
But wait, the next line in the RHA specs *might* be trying to tell us something:
Rated/max power 1/5mW
I *think* that *might* be trying to say that the 100 dB is from a "Rated" power of 1 mW. Maybe. Or maybe not. I will give them a grade of "C". Almost RHA, but I think you aren't really trying...
Please note, the impedance spec is also important. It tells us the load being placed on the amplifier. If your amp can't actually drive the load presented by the headphones, then you might not be able to achieve the maximum volume the headphones are capable of generating before the amp starts distorting. That's why it is important to know the input power for that dB SPL spec. If you need 100 mW to reach 113 dB SPL, and your headphones are 64 ohms - then your amp needs to produce 100 mW at a 64 ohm load - or you won't reach 113 dB SPL. This is why we say that a low impedance and high sensitivity headphone is "easy to drive".