htop is a terminal application which displays all running processes in an ordered list view. There's just one view of htop which displays everything. This avoids needless navigation through different views which usually is very time consuming.
Due to the way glances lists out all the running programs it can be difficult to find a particular one as you would need to search through the whole list manually. This can be time consuming and frustrating when trying to pin down a rogue app.
Conky is editable to the point that there is almost no limit to the designs one can use to display the type of information one wants. Not only are there thousands of themes available on sites like deviantart and gnome-look, but a user can create any type of look they like with a little bit of know...
Conky has a bunch of sensor stat that the user can choose to display such as CPU usage, memory, uptime, etc. Depending on what the user wants to display most likely there is a way to display the needed info when using Conky.
Users can easily set GKrellM to monitor what they like (depending on what monitors are supported by their PC) such as CPU usage (which can be set to monitor each core individually), as well as temperatures and fan speeds.