I won't vote, since I use a mix of the above.
"One of the guys" is usually the motto and the veterans and rookies alike share the glory. I pretty much don't care about what rank they are as long as they are good. Rank's just an added diversion (of course, in the real world it means a bigger paycheck.
Although, I still acknowledge their shortcomings, so it's not likely I'm going to have a soldier with 40 accuracy do a lot of sniping. Probably use that soldier as a grenadier for a bit until the grenades build up the soldier's firing accuracy... up to say 50 or more.
Rookies are always the first to get sent to the front line (the tanks go first if they're available), but some get to hang back with the veterans if they show any exceptional capabilities (high reactions, high accuracy, high strength or they were able to resist a barrage of psi attacks from a sectoid commander).
As usual, the veterans provide long range suppression fire should the scouts spot anything that they cannot handle, or they form a grenade relay chain.
Half of the squad is usually a team of hardened veterans, and the other half are rookies, cycled regularly so they can all evenly get some training. Just a little bit of experience usually goes a long way.
I do, in the end create a 'bootcamp' of sorts at either my engineering base, or my secondary strike base (which doubles as a psi-academy). But, when possible, they see no combat and are merely reserve troops. Those at the engineering base always get a standard issue suit of personal armour, since I like to build tons of those. Got to get rid of those alloys some how.
NKF, narrow minded fuddy duddy who refuses to let go of the past and will not accept anything newer than 1979.