Query string
Query string has some limitation in terms of query string length; this length depends on the browser.
- Opera supports ~4050 characters.
- IE 4.0+ supports exactly 2083 characters.
- Netscape 3 -> 4.78 supports up to 8192 characters.
- Netscape 6 supports ~2000
http://classicasp.aspfaq.com/forms/what-is-the-limit-on-querystring/get/url-parameters.html
Session
Session state can expire (by default, after 20 minutes of inactivity), and the information that you store there can be lost. You can control session-state lifetime using the timeout attribute of the sessionState configuration section.
A session can have any amount of data but if the data is too large then it will affects the performance.
Ref:http://www.codeproject.com/Articles/416137/Understanding-Session-Management-Techniques-in-ASP