OK, I mentioned this earlier, so it's time to actually post on it in more detail. Let's examine the question of whether or not, in general, The Doctor's companions end up better or worse off for having travelled with him. I'll go with my list of who counts as a companion, and I'm considering only companions from official TV broadcasts and not counting any from other media. Also, I guess it's not going to hurt to spoiler this:
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Susan: We know nothing about what Susan's life was like before she started travelling with her grandfather, so normally we'd not have much basis for comparison. However, we do know that he left her behind so that she could stay with a man she had fallen in love with, and since the man in question was a resistance leader on a Dalek-occupied Earth, it seems reasonable to assume that she might have been better off if he'd left her on Galifrey. So we'll score Susan as being worse off.

Ian and Barbara: They were friends and collegues before travelling with The Doctor; they seem to have ended up pretty much as they started, except that they were apparantly a couple by the end of their time with The Doctor--but then, that might have happened eventually anyway. I'll call this one no effect.

Vicki: She was rescued by the Tardis crew from a crashed spaceship, and while she ended up in a time and place that I wouldn't chose for myself, it was her choice. I'd score that as better off.

Steven: He was also rescued from a crashed ship (not the same one as Vicki), and ended up in a time place where he chose to stay. Score that as better off.

Katarina: Well, she ended up dead. Of course, if she hadn't left with The Doctor, she would have likely ended up either dead or enslaved. Still, "definately dead" has to be worse than "likely dead or enslaved", so, worse off.

Dodo: We don't really know much about her. She basically just wandered into the Tardis and later pretty much just wandered out. Call it no effect.

Ben and Polly: We don't really know a whole lot about this pair, either, though they're generally considered better, more interesting characters than Dodo. They end up returning to Earth on the same date as they had orignally left it (though a year or so had passed for them), and they might have hooked up even without travelling with The Doctor. Call it another no effect.

Jamie and Zoe: Though they didn't start travelling together with The Doctor or become an "item" unlike the other 2 couples listed above, I'm dealing with them together because they had the same ultimate fate: their memories of The Doctor were erased and each was returned to their own time. Ignoring the continuity questions raised by Jamie's presence in "The Two Doctors", I'll call this yet another no effect.

Victoria: This is a bit of a tough call. She was already a prisoner of the Daleks when The Doctor first came across her, and without his and Jamie's involvement, that wouldn't have ended well. However, her capture by the Daleks was part of their plan to lure The Doctor, and she ended up time-displaced and a nervous wreck. I guess I have to say worse off.

The Brigadier: Hmm. He had to face threats that Earth wouldn't have been able to handle without help from The Doctor, but OTOH, generally those weren't threats directed at the Brig personally, but rather against all of humanity. I'm tempted to say better off, but for now I'll go with no effect.

Liz: While her situation didn't really change as a result of her adventures with The Doctor, she got more character development than most companions, and was a better person for having known The Doctor. I'll say better off.

Jo: I have a feeling that I'm going to get nailed for saying that Liz was a better person for having known The Doctor and not saying that for Liz (and almost everyone else, too), but I'd say she ended up pretty much where she started, so no effect.

Sarah Jane: Well, The Doctor dropped her off in the wrong town, but more than made up for it by later sending her K-9. I'll say better off.

Harry: Well, not much to say about Harry. No effect.


That brings us to the early part of the Tom Baker era. I think I'll wrap this up for tonight, and post a second part tomorrow or Tuesday. This may end up being in 3 parts. The score so far:

Worse off: 3.
No effect: 10.
Better off: 4.