I have a back/neck problem. Which type of carrier should I choose?
It's not the carrier that's making you feel tired. It's the weight you're carrying. If you hold the baby in your arms for five minutes, it's not enough to burden you. If you feel so comfortable with the carrier that you wear it for an hour (or more) continuously and do chores, it's going to tire you. It's not the carrier's fault, it's the fact that you're pushing your limits.
In that sense, there are two ways to think about it:
1. I select the one with the best weight distribution, so I feel comfortable.
2. I select the one that I put on/off very quickly so that I don't wear it for a long time continuously, but take it off as soon as the time passes that I could bear to hold the baby anyway.
There's no such thing as a carrier that makes the weight disappear. A good carrier distributes the weight better and more appropriately throughout your body, it gets more parts of your body involved (the weight is not hanging from your shoulders, it's not just in your arms, your entire body is involved, your torso, your arms, everything). But the weight is still there, so don't push your body beyond your limits, if you have a problem.
Is the ring sling a bad choice for my neck/back problem?
Not necessarily. Maybe yes, maybe no. As you can see in the pictures, there are ways to wear your baby where no shoulder is involved. Just because the sling involves one shoulder instead of two doesn't mean that the weight is only on one shoulder. It still involves your torso, your waist, and even your chest. What's different about the sling is that you have to wear it correctly for it to be secure and comfortable. There is "right and wrong" and it's up to you. In contrast, the mei tai, or a buckle carrier, for example, will almost never let you make a mistake. These carriers will guide you to the correct positioning somewhat automatically (especially if you follow the method we teach you in Asterakia).
I have a back/neck/shoulder problem, I want something comfortable for a long time and for a heavy toddler.
It would be wrong to suggest anything to you for such a purpose. If you have a problem, follow your doctor's instructions. If your doctor's instructions are "in general, don't carry any weight", there is no carrier that can undo this. If you were to carry your baby in your arms anyway, and for as long as you would do it anyway, then, a good carrier is indeed the best way to go. But it would still be wrong to go for a three hour walk wearing your baby. It would still be wrong to wear a two-year old for hours while also doing chores. That's something many parents do without a problem, but it would be overkill for you, if you're sensitive.
Don't forget your posture
In addition to correct positioning, your posture also plays a role. No matter what weight you carry, no matter how you carry it, you should always try to have good posture, a tight tummy, etc.
Another issue we sometimes encounter with babywearing is that, without realizing it, some parents lean to one side, lift one shoulder, lean forward taking a protective stance towards the baby, or lean back thinking they are counter balancing the weight. All of this is wrong and it will burden you, tire you out.