The 1-26HLG built as a polyhedral is a good thermalling glider. It's much too heavy to handlaunch, but works great off a highstart. Keep it light by covering it with Econocote or Micafilm.
The Highlander thermals well but you have to be sure to build the fuse rigid enough that the tail doesn't flex during turns. Here's a link with construction tips that will give you an idea of what's involved.
The TG-3 is mostly a slope plane that doesn't thermal as well as the Highlander or 1-26.
In the old days (4 years ago), before speed 400 planes became popular, you started with training gliders and that was your only choice. With a Push-e-cat or T-52 you will learn the fundamentals much faster. Then you can move to a thermalling glider. Unless you really have your heart set on a glider, I'd recommend either a Push-e-cat or a T-52. In addition to their training qualities, these planes will thermal, especially if built light.
Best of luck.