Do you think that SharePoint designer is a reliable tool to edit SharePoint pages (like customizing an xslt list view)? Are there any alternatives?

my opinion is when dealing  with an exsisting sharepoint site its prefered to use SPD and if we want to create a new website i will use MS Visual Studio 

I think that SharePoint designer is not more powerful tool that can helps you to finalize a heavy task and advanced tasks.
For Sure there are many different tools that can help you in customizing an XML and XSLT files like for ex.
EditiX http://www.freexmleditorsite.com/download.html or oxygenxml http://www.oxygenxml.com/xml_editor/xslt_editor.html

specially for XML and XSLT purpose you can use following tools 1.
visual Studio 2010 2.
Stylus Studio

To me SPD is the best tool, well integrated with SP.
With SP2013 we don't have to deal with XSLT like we do in SP 2010 and MOSS, SP 2013 is all about HTML5, Jquery, CSS etc..
The Design & preview pane itself is not there in SPD 2013.
Regards, Sudhish