I find a waist/belt holster tucked back a bit (sort of rides just above my wallet...maybe a bit more forward) to be pretty comfortable...but it really depends on what other rig/stuff you're running.
With a "light" chest rig (i.e. RRV)...there's room in the back/side portion to be able to reach/draw if I need to go to my secondary.
In a "heavy" rig (i.e. CIRAS)...the mobility and clearance isn't enough (for me) to reach naturally and draw the pistol from the belt. It'll be a drop leg for that one.
I'm not sure about others...but either you'd want the pistol sitting low and out of the way enough so you don't jam it into your gut/side when you twist/turn/rotate your torso around.
A leg "drop" rig...shouldn't be so low on your thigh that it's hard to reach. It should be as high up as possible and only "dropped" enough so that the pistol can clear the rig that you're wearing. Usually that means that the top of the pistol is right around the level of your front pockets on your pants. To me...it seems retarded when guys have to bend over to reach their pistols in their drop legs.
A buddy tried the MOLLE holster on the side panel of the rig. Unless you set it up cross draw, it's kind of hard to reach to your side and clear the pistol. At least for me...my arm/shoulder isn't flexible enough. Position your unloaded pistol on your side and try to draw upwards...then move it a bit more to the front of your ribcage and draw again. Easier on the front.
I tried the Blackhawk Serpa Strike plate (molle plate) on the front bib of a rig. It works, it's fast. But I was running a single point sling and the sling would get caught in the handle of the pistol grip. Not exactly great for when you need to transition to your secondary and what you just let go (rifle on sling) is blocking your path to it. I'm sure that different slings/stuff might help...I just didn't want to mess with what I was comfortable with. Having a cocked and locked 1911/2011 pointed at your weak side arm when holstered really made me nervous. It shouldn't go off as you bumble through the bush...but you never know about mechanical safeties right? Didn't worry with a decocked 226 type pistol though.
The one thing I didn't like about putting the pistol/mags in the front (i.e. on bib, in a front pouch, forward mounted molle on rig) was laying in the muck with it. More than once we were laying in swampy depressions and I was thinking..."this can't be good for my gas pistol".
Don't forget about positioning your pistol mags. Having an extra mag on your drop leg is near impractical to get to in a real hurry. Putting them up front will jam them into whatever you're leaning against. Not putting a flap over them...and they'll fall out in the field.
Have fun, best of luck finding a rig. Get out to some games and ask the guys what they're running and how they like it.