Which is more common.....

suppose this will very much depend on the A/C you're flying, how far, at what altitude and in which weather conditions...

I bet very few jets fly IFR,......would just sound unlikely to me.

All Airliners (as far as I'm aware) fly IFR. The speed, altitude, passenger numbers, scheduling, safety factors, as well as 100s of other factors make IFR flight the only feasible means of navigation for an Airliner.

VFR is more relevent to GA (General Aviation, or lighter aircraft) where visual reference (knowing where you are by looking out of the window) is more practical of possible. However, many GA aircraft also fly IFR, where the weather makes VFR flight not possible, and where the pilot is suitably rated for Instrument flight).

You flew in a 320 from Bahrain to AMS at FL110?? I do not know how far it is but would imagine the burn was rather high! Jets- Boeing, Airbus whatever are not designed for much under FL180 which is where TP's are king. Only reason I can think of for flying this low is if there was a problem with pressurisation etc. Which airline was it?

it was KLM...Royal Dutch Airlines. BTW, Im not sure about the distance, but it was around 5.5 hours

All flights above 18000' are IFR period. The reason is because min VFR conditions require 3 miles visibility and 1000' ceiling, if you are at 18000' with only 3 mi vis you would not be able to see the horizon.----- slant visibility must be even higher at that alt to see the horizon You would have to rely on the instruments alone to keep you upright and strait. That is the definition of IFR flt. The only thing you can trust in IFR flt. is the instruments. Even if your body is screaming at you saying "YOU'RE GOING RIGHT! NO WAIT, YOU'RE GOING LEFT, UP ,DOWN---- UPSIDE DOWN! don't believe it. It will get you killed.--- spatial disorientation they call it. That is exactly what killed JFK junior in '99. so believe ONLY your instruments. I am a real pilot and have also studied many NTSB reports on aviation accidents, the afore menrioned condition is the primary cause of GA accidents in IFR cond. They are generaly always fatal as well.

P.S. I forgot to mention most flight below 18000' is conducted under VFR conditions, unless you are on an IFR flt plan. All airlines work under IFR plans from T.O. to landing for separation safety purposes. --- Keeps mid- air collisions to a minimum.

All flights above fl180 are required by the FAA (Federal Aircraft Association) to be IFR. One reason is because you are so high at that altitude that it is hard to see the ground. The ATC in the real world doesn't make you make as many turns.

JAA rules are slightly different but I think Leadfoot has covered the bases with his post and as FS is based on the US system there is no real point in me explaining "our" better rules!! Joking aside I just wanted to point out in continuation of Leadfoots post that over here I think the biggest killer, or certainly near the top in aviation is controlled flight into terrain. Keep your charts handy know what the MDA is along your route.
Back to the original post IFR/VFR I personally prefer flying IFR as it is more challenging and rewarding when you pop out of cloud and the runway lights are straight ahead......usually! VFR is good fun as you are left to your own devices, turn the GPS off and fly by the map.