Besides selecting an appropriate package for your operating system (Windows, Mac OS X, or Linux; 32 or 64 bit), you should take into account the following considerations.
Should I download standard, full, or NGS package?
Explanation of the tip above: Some tools are embedded into UGENE as external. To be launched from the UGENE graphical interface, an external tool needs a corresponding executable file. The list of the external tools can be found on this page.
The standard package does not include the tools, whereas the full package include all the required tools.
The NGS package, besides containing the external tools, contains sample data for the Cistrome pipeline (hg19 genome, reference genes, etc.), so you can run it out of the box.
I have Windows. Should I download installer package or portable zip bundle?
If you have administrative rights on Windows, use the installer package. It will make integration with your Windows system more tight. For example, it will add associations for bioinformatics formats supported by UGENE, so that corresponding files are opened in it by default.
I have Linux. Which package should I use?
If your Linux is not Ubuntu or Fedora, you can use the installer package too. Otherwise, for more tight integration with the systems, you can install UGENE from corresponding repositories, following these guides: