First Lightweight Pack

I am also going to check out the ULA Circuit.

Might help to ask a question if you want advice about something in particular, but advice really doesn't mean much when it comes to pack choice, anyway. All the packs you list are familiar names here, liked by some, and disliked by others. Yours has to fit your gear, and most importantly, YOU, though. Noone else can tell you which pack will do that. They're all good and they're all bad..for someone, somewhere.

When I last pack shopped, I took my gear in a tote, and tried everything I could get my hands on for months, both locally, and on road trips. Good way to weigh your options, if possible.

I agree with Owen. Try as many as possible, I've tried most and nothing fits me like HMG.

Good luck!

If your interested in an Exped Lightning 45 I have a barely used one for sale for 130$

Go for the seekoutside unaweep (http://store.seekoutside.com/unaweep-3900-backpack/). They offer it in cuben if you want to save even more weight. It is the most comfortable pack I have ever used. It will carry anything you are physically capable of but is so adaptable and compressible that is works great with smaller loads as well. With cuben you are talking at most 1/2 a pound more than the mariposa for example with a vastly more capable and flexible suspensions.

I have a more defined chest for my size and I found the s straps very comfortable from ULA. I had tried all kinds of packs but ended up with the ULA Circuit personally. I get pretty much 4 season or close to it with this pack.

First you need to finalize all your gear as much as possible. Measure the weight and volume, take into consideration a bear canister if you will be using one. Now assemble all the food and water you will be taking on your longest trip. Now you know the weight and volume of everything you need a pack to carry.

I need two packs. One for short trips and another for long trips/winter trips.

Going to agree with Nick here. The pack is really going to be something that's a product of the rest of the gear you're going to be carrying (and the corresponding weight and volume).

Realistically, the options you floated above are generally well-liked around here, especially the Mariposa and Circuit, and will probably fit your gear if you're coming from a 65L pack. (Assuming that your weight isn't otherwise crazy and that you didn't have the pack bursting at the seams.) Thus, you're probably not going to go horrifically wrong with any of them. (I should add that I don't have a ton of experience with either model, and am an MLD Exodus user myself.)

Only thing I'd caution is to be a bit mindful of space in the Lightning 45. If you were more or less filling up that Gregory, the drop in volume is going to be pretty substantial.

Thanks everyone for the advice. I am going to try a variety of packs and see what fits me and my gear the best.