So I currently have my Garrison Bespoke suit, and my John Ferrigamo suit is still being made. Here are the differences I have noticed so far.
Garrison Bespoke does muslin fittings on their custom suits. They have a wide variety of fabrics to choose from and I chose a Dormeuil Amadeus light navy fabric. It's a gorgeous fabric but maybe a bit delicate for my needs. The fit of the suit is very nice and trim, but could potentially be a bit snug at times. However, the cut of the suit is great and modern and the tailor was very focused on what I was going for. A nice added touch was a wonderfully hand-sewn Milanese buttonhole.
John Ferrigamo does basted fittings on their custom suits. Their custom suits are cut off of five different patterns. They have a wide variety of fabrics as well and I chose a Holland & Sherry charcoal fabric from their durable line. John Ferrigamo is a little more conservative in the style of the suit, but still does very trim suits. Their specialty seems to be big peak lapels, and their signature is doing buttonholes on both lapels. John Ferrigamo did hand-sewn stitching and buttonholes for my suit.