This is a list of gutter sealers from best to worst. This is not a list backed up by some scientific source, this is purely from my own personal experience.
Urithane sealers Distributed by the industry leader OSI.
I have had a lot of luck with this particular sealer because it sticks to all kinds of surfaces. OSI Urithane works well but it is very messy. If you get this stuff on your hands it is impossible to clean off. It can be used for roofing as well as on gutters.
Geocel 2300 is a product I have been using for a long time. What I like about Geocel is that it comes in so many colors so that you can match it up for for different applications. It sticks to many surfaces and lasts for a long time. This is only available from special dealers like my supplier Ryan gutter. However, I did recently find it sold on Amazon.
Professional sealer mate
What is Tetrachloroethylene and Hydrocarbon Resins? I have no idea but they work really well in Seamer Mate. It looks just like Butyl but it is a lot thicker. I have used this caulk to seal new gutters and to reseal old ones.
Butyl caulk is the go to sealer for new aluminum gutters. It works okay for brand new gutters but not very good on older gutters as a re-sealer. Butyl is very watery but this is supposed to be a selling point because it flows into the gaps to seal everything up. Butyl caulk is made by many different companies and is easy to find.
I remember way back in the 80's when DAP silicone caulk exploded on the scene. It was all the rage. There seemed to be no leak that was beyond it's reach. Those of us in the home improvement industry felt like we were stepping into a bold new world. Unfortunately Silicone does not work well on gutters. Eventually it dries out and loses its bond to the metal. When you have to reseal a leaky gutter, you must re-coat the area with more silicon because other sealers wont stick for long.
Roof cement is the worst sealant to use for gutters. I really haven't found a good use for tubed roof cement other than making a huge mess. As I mentioned previously, roof cement is useless if is watery enough to squeeze through a tube.