Actually, the best approach is the one that you will stick with! The reason I have said that you need no weight with negatives is because the point of my negative is to manipulate time. I like the idea of spending longer on the bar and you can do that without weight. If you can come down from the bar in :10 for three reps, and it seems easy, then go for three reps of :15. If that's easy then go for :20 per rep. However, adding weight is fine as long as you are not dropping from the bar too quickly.
I like the idea of training Chin-ups three times per week with one time (perhaps the middle) using "some" weight.
My biggest problem with those who want to train with weight all of the time, but are training for one max set of reps is this: You don't know how your body is going to respond at higher reps unless you have been there!
Yes, the stronger the better, no question. However, to perform one high rep set to your maximum takes the proper type of training. A question that I have repeatedly asked (to those who really, really hate my Chin-up routines) on this very subject: How do you know how your body will react to a 20+ rep set (for example) unless you are training higher reps? The answer is, you don't know how it will respond and that is one factor which you don't want to have to deal with when you are going for a personal best.
For example if one 20 rep set of consecutive Chin-ups takes :30 to :40 seconds to perform there are a host of things going on inside your muscles, which are basically different than when you perform say 4 reps with a heavy weight which may take you :12 to perform
When you train in higher rep fashion you get used to training when lactic acid levels are quite high. In fact, some would argue that you actually teach your body how to deal with the lactic acid more efficiently. There might be some truth to this as I have seen guys who can out rep me with 100lbs. but I leave them in the dust when it comes to higher rep sets. It can be argued that I am able to do this because this is what I train for.
In addition to this you are also building your endurance fibers which will carry you to ever increasing numbers if that is your goal.
Don't get me wrong I go off the high rep training relative to Chins and love to train with some serious poundage's throughout the year. However, that is not the bulk of my training with this one particular movement.
I have been involved in many heated debates over this very issue...on this very forum. However, I always say train sport specific! If you are trying to gain higher numbers in Chin-ups don't waste your time doing T-bar rows (a great movement by the way). However, T-Rows won't get you the higher numbers you want relative to Chin-ups. Same goes for training with weight in the Chin-up.
I will end where I began: if you want to perform one of your three Chin-up days with weight no problem. Make sure the weight is not overly cumbersome. For example, if you can perform 10 dead hang body weight Chins keep the weight around 10lb. to 15lbs. This will be plenty of extra stress and will indeed help build plenty of muscle which will help you a great deal.
Just make sure that those other two days you are performing 4 to 5 sets of high rep Chins (a percentage of your one set max as per my original post 1-04).