If you intend on solo play through most content survivability is a huge factor. In that way, Tanks have the highest "toughness" levels in the game, and they make solo play more practical.
You should be able to deal with most, if not all content, on your own. Other Archetypes such as Brutes, Scrappers, and Stalkers can also solo effectively, Tanks can do so with less time spent getting an optimal build.
As Tanks are Melee based, their Offensive Sets offer powerful animations in most sets especially Super Strength, Battle Axe, War Mace and Radiation Melee. Almost all the sets are about the same damage wise but I would look for ones with multiple "Area of Effect" powers as these give you an edge when fighting groups and add to the feeling of power when fighting.
With all that said, I have seen effective Solo Characters from all Archetypes and Most Sets, I just believe Tanks are Easier to build to that end. Play what you find enjoyable and try as many as you wish till you find the best one for you.