So, the question of this thread is "Who controls your Animal Companion or your Familiar?"
Most people that I know would just say "Oh, well, the player does, of course." But that feels kind of like a cop out to me, especially since these creatures have their own intelligence scores that start at 3+ giving them a measure of individual sentient thought, thus meaning that they should be free to make their own choices and have their own fears, likes/dislikes, quirks, interests, and opinions, albeit ones that keep them as BFFs to the Druid/Ranger/Wizard/Sorcerererer/Witch/Whateveritis that they're bound to. Though, just because it's bound to you, doesn't necessarily mean it's going to follow you around saying "Yes, Master. You're quite right, Master. You always know best Master." while drooling a lot. There are times (Especially with high level sorcererers who aren't necessarily the brightest of blokes) when their critter could express an opinion differing from its master's which might even be a better idea than the one the master had.
My personal thought is that the player should control the actions of an Familiar/Companion while in combat, since it allows for better strategizing and employment of the critter, (Though the DM should take over if they try to make it do something suicidal for no really good reason.) while having the DM play them when they're just sitting around the campfire or running around town looking for things, because it's entertaining when you have to restrain your wolf from running into the butcher's shop cause it smells dinner.
Thoughts?
Without waxing verbose, I'll simply say that your personal thought matches up with mine (and seems to be the group preference also).
Although I do tend to ham it up with familiars when running a game (in a good way), and in exchange for that privilege I usually grant it an extra feat, or a point of INT, or something of that nature as a RP reward for the good-spirited player.
As both a DM and a player I can say that I've never been involved in a game where the player isn't in charge of their animal companion or familiar. Frankly as a DM I don't want to run your snake or wolf or tyrannosaurus. I've got plenty of more important things to do each round. As a player, it's a statistic in my character sheet. A rogue gets to decide when his dagger goes for a sneak-attack and a barbarian gets to decide when his dander gets up so why shouldn't a wizard get to decide when his salamander crawls out of his pocket?
That all said, two items of addendum:
1} If it's situationally appropriate, a DM can "put words in his mouth" or override actions. This really mostly comes into play with familiars with an agenda. Like say... imps. As a DM, I occasionally deliver knowledge or experience that familiar would have, in-character. Usually the familiar says what the player says it does... but sometimes the familiar knows more than the player does. Shrug.
2} Leadership. Depending on the circumstances this can go either way. My groups have played it both ways. Currently I'm running one of my players' cohorts as a DMPC to give myself an in-character voice. (That game is one player with three PCs, plus me as DM. So a second in-character "player" voice really helps.)
Otherwise... hands off the familiars.