Which strategy would be the most effective...
The biggest problem with freerolls are the "Crazies" who go all-in on almost any 2 cards, in order to avoid them you need to play super tight, only calling when you have a monster hand, and even then it does not always win.
Once the "Crazies" have been eliminated then the players become more serious and will play Poker, unfortunately if you get to that point then you could be short on chips yourself, So then you need to go all-in, to accrue some chips, either by stealing blinds or hitting lucky and doubling up.
It is never easy to win a freeroll, but just keep in mind "it's not cost you a penny to play" So no damage done to your
bankroll.
I always played with an attitude that if it's free! Then all wins add to your BR Whether that's 10 Cents or 50 Dollars, so don't look a gift horse in the mouth, and if you bust out to some idiot that calls your All-in with a 7/9 off suit, that spikes a straight on the River, So What!
It hasn't cost you anything, So what's the point in complaining about "Rigged Games" or "Bots" playing at your table. Bad Beats and Coolers are all part of the game, and once you can accept that, then you can start enjoying the game, whatever the outcome.
What is the best strategy for playing Freerolls? Just enjoy them!