Don't have first-hand knowledge of either model, but Garmin makes a great GPS, and Lowrance was the first sonar on the market back in the 60's. Lowrance has refined their sonars for 50+ years, and Garmin should have stuck with what they did best. Just my opinion after a couple of each.
I have tried out both of those units. The Striker is very good, the Hook so shockingly bad that I cannot believe that Lowrance puts its name on it. I had a 20 year old portable Lowrance\Eagle that worked better. But buy both from Cabelas or Bass Pro, try them, and return the loser. Depending on your needs, Garmin is now including QuickDraw Contours on the 4 Plus, allowing you to create your own maps. Since none of the map providers have decent maps for Colorado, it is a great feature. Garmin does have a map sharing community, but almost no one is using in in Colorado. If you want to use community maps rather than making your own, then Lowrance might be a better choice, but go with a better unit than the Hook.
Being able to make maps and or update the maps you've already made is priceless.You should see the details I have for Aurora.Heres the kicker . . . .I add or update my own map everytime I go.The GPS available today is spot on.