PFD

It depends on the weather conditions. I voted for the airspeed indicator but with IFR conditions, my vote would change. 😉

You can sense most things except your speed, so I voted airspeed indicator.

Agree with Crash...but also it depends very much on the weather. I'd prefer to overspeed than smash into the ground 😉

Airspeed indicator ❗ ❗ ❗ 😀

VMC-ASI
IMC-AI

alll but i picked altimiter and if you for get your flying to denver the mile high city or flying over it in a cessna in ifr conditions ud be in the ground

In the event of a primary flight instrument failure, I'd rather pray the attitude indicator would still keep working. For me, maintaining orientation thru instrument and visual means is a primary priority. In case of disorientation especially in IFR conditions, the AI would be a great help in recovering the plane back to straight and level flight. CFIT is a major concern and the terrain is still the champion plane killer, more deadlier than a Sidewinder or an AMRAAM air-to-air missile.

For me, airspeed control is just a secondary priority since we all know that an airplane will stall in any condition regardless of the plane's airspeed and attitude. Should my airspeed indicator fail, I could simply cross-check my engine control and performance instruments like the tachometer, the manifold pressure indicator and RPM gauges to verify the plane's power settings, therefore getting a rough "guesstimate" of the airplane's airspeed. You'll acquire this skill as you log more hours and become attuned to the characteristics of the particular airplane you're flying. Getting a feel for the airplane, as the fighter aces would describe it.

Should you require more speed, simply increase power. You'll know if you're flying too slow and right at the edge of a stall - signs are present: the stall warning horn will sound, the plane's flight controls will be mushy and you'll feel some buffeting as the airflow begins to disrupt. To recover, simply add power and cross-check the AI to make sure you're maintaining a straight and level flight, and not about to execute a power dive.

I don't know if the technique I mentioned above is an airline standard procedure stuff or what but I'm a believer in the concept of attitude instrument flying. Of course, I could be wrong on this one as actual flying and flight simulations are 2 different things. What works in one may not be the effective solution in the other. In the end, it's about the man behind the machine.

Attitude + Power = Performance

I agree, I choose attitude. If you're flying trough clowds, your inner ear can fail you. You think you're flying strait although you're actually doing an inverted flight. You don't need airspeed or altitude, you can judge those, but you don't really need to. Just rely on your attitude indicator and keep a light glideslope, you'll come done under clowds/fog if there are any, and be able to judge your speed compared to the ground, and altitude doesn't matter, you just want to bring the thing down. You can estimate a good landing patch, and make a bumpy/crash landing. But you're alive.