I mainly use the Smart tool. I use the Split tool regularly too, but not via the 4th button on the Tools module, because it reverts back to the default tool (Edit tool) which I never use every time a project is loaded. So, I just hold down ALT to temporarily enable the Split tool while I'm on the Smart tool. I use the Mute tool as well quite often these days, in order to fix results caused by a couple of bugs which I'm not going to mention here. Since there's no key to hold down to temporarily enable the Mute tool, I have to click-hold the 6th button that by default selects the Erase tool (which, again, I never use) and drag down to select the Mute tool, which is a littler quicker than looking down and locating F10 on the keyboard and hitting it twice.
I wish the module could remember the tools I selected last and regularly use even after the program is shut down. I also wish I could assign these tools freely to the buttons just like we can assign available commands freely to buttons on the Custom module. The Select tool and Move tool, which, again, I never use, are meaninglessly occupying two of the big six buttons, wasting precious space on the crowded Control Bar (I use the "small" version of the module, but I think I can do with only 4 buttons if the tools were freely assignable. So an "extra small" version with just 4 buttons would be nice for me).
Finally, I've always wondered why the Zoom tool and the Scrub tool aren't in the Tools module. Aren't these also "tools" that can be used in the Clips pane? Why left out? I know they can be enabled by the Z and J key respectively, but they have the right to be included in the module and be used by more users. Personally, I would use the Scrub tool more often if it worked on a lane basis (not on track basis) and could be assigned to one of the buttons in the module.