Who do you use the Master Balls on?

In each game, who do you use the master balls on? As for me...

Red/Yellow/LeafGreen: Mewtwo
Crystal: Suicune
Emerald: Rayquaza
Platinum: Heatran
HeartGold: Ho-Oh
Black: Kyurem
Black 2: Kyurem, Heatran

Firered: Mewtwo
Crystal: Suicune
Emerald: Rayquaza
Platinum: Moltres
HeartGold: Ho-oh
Black: Kyurem
Black 2: Kyurem

I usually use them on roamers. If the game doesn't have a roamer or I have no intention of catching it, I just save it for something I'm too lazy to actually try to catch, like when the game forces you to catch the mascot legendary.

Usually on a roaming legend or a shiny pokemon, I will use masterballs on them.

... I find I don't use masterballs XD
It's like the Queen in chess, I feel it's so valuable that I need to save it for something really worth it, then I never end up using it. Usually it just ends up as 1hp sleeping ultraball spam, and my Masterball goes unused.

I used to use them on any legendary pokemon that I really wanted, such as Rayquaza, Mewtwo, and Lugia. Now I use them for roamers like Latios and Entei since they're much harder to catch.

Roaming legendaries mostly, perhaps on one legend I absolutely want, but I worry that I can't catch. Like Regigigas in B2.

Not counting emulator games (since its so easy to cheat and make hundreds of M.B. appear on PC) -

I have not used my master balls so far, I want to save them for a rare shiny - so far none have appeared in any of my 3 games. Maybe my only exception would be a legendary Pokemon but after I have ran out of all other Poke Balls I have with me at that moment.

I usually save it for roamers or Legendaries I know are hard to catch.

When I first started playing (Gen II), I would usually save them for the game's mascot or some other legend. Now, I don't use them at all. Unless I need some filler for a quick trade.

I've used them mostly on the main legendary of the game. Like in Red and Yellow I always used it on Mewtwo or in Gold/HeartGold I used it on Ho-oh, and in White I used it on Zekrom. The only time I used it on anything else was in FireRed when I used it on Entei. Since it's a roaming Pokemon I figured it's only easier than chasing it around. Plus with the Roar glitch in Gen III games I figured it might be my only chance.Now I've been trying save them for the roaming legendary or one that's hard to catch.

I used to use it on the title legendaries, but I've grown to the point where I don't use it at all.

I remember accidentally using it on a Doduo back in Gold the first time I got it.

Just shiny pokemon. And even then only as a last resort, or if it's a Pokémon that can flee/ explode ect.

Other than shiny Pokemon as well, the only times I can recall using a Master Ball was on Mewtwo in Yellow, and on Latias in Sapphire. I think that currently on HeartGold, I've got 8 Master Balls, transferred over from other games I didn't use them in (one of which I also won from the raffle in Goldenrod).

This one time i fought Dialga down to the wire, and ended up using it on him, but then i turned it off and back on and chucked a quick ball first turn. Ridiculous catch that was.

I like to use normal pokeballs or any type of ball that doesn't give you a higher catch rate, but Just to piss of my girlfriend I used my masterball on a Magikarp. ^^

I use it as a backup in case I spend hours trying to catch a legendary and I keep failing. In Silver or Crystal I used it to catch a Chansey and in Pearl I think I caught Mesprit with it (but I could be wrong), so those were my weirdest uses for it. I clearly remember in Blue that I'd use it to catch Mewtwo because even to this day I hate the Cerulean Cave.

I tend to save them in case of shiny Pokemon that tend to teleport/self-destruct/explode.

I didn't ever use them. Nothing was worth it, and I keep them as a collectors item. I suppose that defeats their purpose, but I enjoy the struggle of catching things.

If I have to capture a Pokemon to advance the game, then I'll just use it on that. To my mind, Reshiram is the only one I can think of off the top of my head, but there are probably others that I'm missing.