Huh, neat to see all the replies. I figured Gold would edge ahead and it seems like it did.
For myself, I promote to reset 90% of the time, so I'll bum around on Silvers with my low levels until I have whatever core powers/ranks I feel necessary to competently go up to Gold/Plat.
I Gold with kits I'm either new to, weak on, or less than lvl 16ish. Or if finding a Platinum pug lobby becomes a stressful exercise in futility... oooor if I've made a kit that I want to take to against a specific faction (Geth for instance with synthetically potent abilities.)
By far for me, the most fun I've had in this game is when I rock a Platinum with a complete stranger or three. I love the challenge. Particularly I remember having to completely readjust my tactics, but also some over all strategies I employed in the game when I was first introduced to phantoms creeping around behind me while I was concentrated on that Geth Prime. Died a lot before I really started to "Watch my six" in platinums regardless of who I had it set to. I like the credits, and I love the feeling of blowing up bosses like they were mooks when you get at least 2 kits capable of working well together, and players who're using some seriously equipment/consumables.
Platinums offer to me a challenge no other difficulty does. I don't have to scorew'hore to enjoy it, I just like working on the difficulty with funky kits. Did a pug plat on Ghost the other day with two Asari and two Drell (I took my drellpimpguard out of the closet) Everyone went down soooooo much, but everyone was quick to revive everyone else, so the foolery was fun instead of... foolish. I definitely did not score top, but I also definitely enjoyed myself.
...now that being said, by far I have had my worst moments in Platinum as well. It's much more hit'r'miss, with greater extremes at both ends. It's my favourite, but I don't constrain myself to only playing Plats. (I'm looking at you box'o'shamers. That method of playstyle is sooooooo boooooring and foooorever-taking.)
It's interesting looking back at this now.
I'd say Gold wins flat out after re-glancing through this topic.
I barely touch silver now, even if I promote I'm at the point where I'll save millions beforehand to buy Recruit/Reserve packs. I'm almost exclusively platinums myself now. Think I've done about 95% platinums and 5% golds in the past several months.
The thing that's changed a bit for me is my take on box-o-shamers and camping. If I see a crew working together fairly well I'll stick with em. The population is lower and my tolerance has gone up as a result. I think I take the game a lot less seriously now as well. Only 14 UR's to go for the first legitimately maxed PC account in forever. (trolol.)