1) All prints in the same size matte and frame - matte border sizes will vary slightly.
Both
#1 is great for two reasons:
1) It will speed up the framing process on the front end a bit as you can quickly chop all of your frames, mats, backing, and glazing to the standard frame size. Depending on where you get your frames it may cost lest as well, as many framing wholesalers offer discounts on quantities of the same size frame
2) It makes things much easier to hang on the wall
The downside to #1 is each of your mat window openings is a custom size. You can reduce this pain if you tweak your image area sizes as much as possible to get consistency (sometimes just adding 1/4" or 1/2" to the image size is enough to make it match another image, and doesn't hurt the asthetics).
If you do go with #2, there is one advantage:
1) You can ensure a consistent mat width for all your photos, which makes cutting the windows MUCH easier if you have stops on your mat cutter.
I recently framed 7 images to hang in my office and took a mixed approach. Four of the images are in a standard 11x14" frame and hung neatly as a series on one wall. The other three images, which vary in size from 6.5x20" to 15x17.5", are hung in frames that are custom sized to allow a 3" border. Hung with the center lines at the same height it looks great.
Neil