Gonna ditto the "fuck Wade's idea" from others. Not to put anyone down - that's just my view. It's not a group decision between everyone involved - it's your decision and yours alone. Doesn't need be discussed in any format other than you talking to the various options.

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If I were in your shoes the first thing I'd do is rule out Virginia. You've committed to your puppy and you love the wee adorable beauty. 

I'd also try as hard as I could to dismiss the influence this unwell friend of yours is having on your decision. It sounds like they're a close friend; I'm sure they wouldn't want you to stay based just on them. You can stay in contact and see them when you can - and they know you'll be there for them in a crisis. As you know yourself - you have to make these sorts of life decisions for you. Not for anyone else.
If you really can't rid yourself of your concern for them (and are the type of person who won't regret or feel resentful if you make a decision based on your friend and it turns out to be a bad decision down the line) then I guess that's a big plus for whichever option is closest to home. Another added bonus is being close to your parents - trust me when I say that you [i]need[/i] a solid support network when moving away (particularly for the first time). Even if you're an introvert - you need people you can rely on for emergencies and to help get you acclimatised to a new place. Being near your parents and home is a huge "pro" in this regard.

For the same reason you need to think about how good these friends are. If you're to move far away to live with them they need to be both reliable and consistently fun (or at least chill) to be around. Just because you get along with someone as part of a social circle does [i]not[/i] mean you could tolerate them as a flatmate. I couldn't live with many of my closest friends because we'd drive eachother mental (in the bad way, not the "oh you!" way.)

Also to consider is job opportunities. You said you're a grad student - are there opportunities for work in whatever field you studied? Or rather: whatever field you're currently working in and would like to pursue? Don't take word of mouth as gospel - look for job opportunities in each place online. Where has the most openings you're eligible for? What's the pay like? What's the cost of living like in that area by comparison to the pay? I have no idea but S.C could be half as expensive to live in as C.O and that could be a factor to consider as well.

As Awson said... there are a lot of factors. I've tried to summarise in the TL;DR.
Personally I'd echo others and - assuming the people there are indeed reliable and fun etc. - I'd choose Colorado. Of course I don't know the job/cost aspects though.
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TL;DR: Factors to Consider (in order and bolded if especially key): 
1. [b][color=ed1c24]Dog[/color][/b] -  based on what you've said this contributes the most to no. 3 so I'm putting it at the top.
2. Viability. [b][color=ed1c24]Job opportunities and cost of living[/color][/b] in that place. If you aren't sure you can afford it or job opportunities are scarce - don't go. I know putting this above no. 3 is controversial-seeming to some happy-go-lucky folks but from experience... I live somewhere I can't afford. If you're destitute and stressed and can't find a job and can't feed yourself or your dog and blaaah blaaaah blaaaah you automatically violate no. 3 anyway - no matter how positive a person you are.
3. Happiness and wellbeing. [b][color=ed1c24]How reliable and fun/chilled out are the people you're moving with?[/color][/b] Are you positive you'll enjoy living with them? Do you have a good support network there? [b][color=ed1c24]Don't be reliant on just one person (the flatmate you're moving with).[/color][/b] Do you think you'll like the city (weather and atmosphere and things to do etc. etc.)?
4. Your friend at home (should you be unable to shed your worries about them).