Which faction(s) to invest in?

I got the game a few days ago, started with Skellige, it was pretty decent through damaging, bloodthirsty and self boosts through damage… buuut I found it very susceptible against locks (especially Nilfgaard), I was basically crippled. Also the Patricide leader was really great, but everyone has Grealt, so.. 😩

Then I played Nilfaard a bit, it was okay, but I have a hard time picking 1 stategy for it since it has so many options; stacking poisons to take out units, or stack spies and reap the spy-related benefits, or stack locks against important enemy units, or just stack numbers on my own deck. I don't know what to do with it.

Then I played Northern Realms and so far I've been getting good results from it. It's fairly easy through stacking booster units, Inspired cards, and cards that keep going each turn (like that ship that spawns a volunteer each turn, or cards that boost adjascent units each turn, etc). And the good thing about it is that I have so many of these cards that synergise through boosting that one or two locks don't pose as big a problem as it did on Skellige (at least in my experience).

I have gotten a few kegs for Northern Realms in the reward book, but since those skill point keys are not easy to collect, I'm hesitant about investing too much into it if it turns out to be not as strong in higher levels. And I also don't want to lock myself into one faction, I wanna play them all, BUT I'm afraid of spreading my resources too widely and not getting good results, or investing in one faction that later turns out to be not so great.

I haven't played Scoiatel and Monsters yet, but I will soon. So I'm wondering if you guys have any advice on whether to invest in one faction or spread my resources on all of them or just focus on two or three factions? Should I buy faction kegs or neutral or ultimate kegs with my ores? There's a shitload of rewards in the Reward Book too and I'm not sure which direction to go in that either 😩

Sorry for the long post, any advice or tip is appreciated =)