My SDK Manager shows two platform tools, one which comes under the folder 'Tools' which has revision 22, and the other which comes under the folder 'Tools (Preview Channel)' which has revision 23rc2. When I download and install one, after rebooting the SDK Manager, the other one comes as not installed and vice-versa.
So if only one can be installed which one should I go for?
You can use only one version of SDK platform tool at a time.
Under tools the Android SDK platform tools means those tools which have been fully developed by Google are are now stable builds.
Under the preview channels are the one which are under development and are in beta stage, they are meant for advanced developers to give them an idea about the new releases and features yet to be offically released.
So, you must go with sdk tools under tools unless you are ready to take in account for those extra features and for some unknown bugs.