First hiking trip, need help choosing a bag

Are you planning any pre-hikes? They would be important to testing your gear for comfort. It would also tell you if 50L would be enough. I actually prefer a slightly larger pack for 5 day treks, but that is what fits my gear well.

Do you have access to any stores that carry these packs? If so you can go and try each one out. If you are not sure, do some digging and see what stores in your area carry. There ought to be someplace within an hour drive that has packs you can try.

Are you planning on camping, or actually backpacking (ie moving daily with your pack vs just walking a short distance in an staying at one place while you might day hike out of it)? Fit matters most the more you plan on moving. Spike campers can tolerate more weight, and perhaps discomfort, on the way in as they set most of it up in camp and then conduct their hikes.

Some things to consider as you try to narrow the search down are: pack weight, adjustability of the suspension, your size so that your body type matches the pack, options you might want (where are the outside pouches, does it have side zippers or bottom access, etc). This is NOT an all inclusive list, just a few things for you to think about.

Both packs are fairly well reviewed and liked by many hikers. My son has the Terra65 and absolutely loves it. When it wears out he'll try to find another one just like it. That said, you could find it uncomfortable.