Personally I like both power level and points rather equally. Points are definitely better for more competitive scenes, but that does not mean you cannot create competitive lists from power level alone.
Power level gives you more bang for your buck, with upgrades nearly all included in the power level, e.g. a mortis dread with x2 twin las cannon at 8pl a damn steal.
While this is true, you also have to keep in mind that certain units have steep power level costs. If you were aiming to make, say, a space marine 1st company strikeforce or a Dark Angel deathwing army each terminator squad runs you about 12 power per five terminators. Necron destroyers are each 3 power, so the same concept applies; as opposed to how dirt cheap guard infantry squad or ork boy squads are.
Power level, in my opinion, has a larger focus on what units you bring to the table rather than what each unit has.
Points gives you more flexibility with unit composition but runs up the cost quite a bit with upgrades and non standard squad size.
That first part is and isn't true at the same time. Under power level your not forced to stay strictly by certain squad sizes; I could take a 21 man unit of imperial guard conscripts, but power level wise it will cost me the same as a 30 man unit.
As for the second part, this I do agree with and feel it is more the focus on the roles your units can perform. Like before I could take a unit of terminators, running me about 200 points with no additional upgrades, but what can they do?
Starting off I'm probably going to go power level because of the ease, what do grizzled campaigners prefare/play?
I think a part of it lies in the army you play. Some armies, like Orks or Guard or Tyranids, can bring a very good selection of units even at lower power level while armies like marines, Necrons, and Eldar do better with points (though you can create good lists with almost every army in either style.)
Points. ALWAYS use points. At least if you're looking for an equal(ish) game.
I'd argue that power level games can be pretty equal. I mean try making some 80 power lists and you'll find they all tend to be around 1500 points. (I actually did this with 75 power across five armies and they all totaled between 1325 and 1450 points.)
Power level is decent if you're quickly setting up a narrative game, but the mechanism sucks for actually balancing things. The free upgrades you mentioned play a big part in that, as armies that can bring a lot of upgrades have no incentive NOT to kit things out with everything and the kitchen sink.
Keep in mind that in some cases, some of those upgrades are locked behind increasing squad sizes, which would in turn increase power level. Then theres also the steeper power cost in certain units, like a leman russ or squad of terminators.