Both should work.
4.2(3) may have better bug fixes than 4.2(1).
but do we need to upgrade from 3.3(5) to 4.2(1) and then from 4.2(1) to 4.2(3) or can we directly upgrade from 3.3(5) to 4.2(3)
thank you Sankar for your response. Please also let me know if there are any SR or ES which i need to install after upgrading to 4.2(3).
Just to add a note to Sankar's excellent info,you can upgrade directly from CCM 3.3(5) to CCM 4.2(3) Have a look;
If your server runs a version of Cisco CallManager Release 3.2 or earlier, you must first upgrade every server in the cluster to the latest version of Cisco CallManager Release 3.3 before you can upgrade to a version of Cisco Unified CallManager Release 4.2. For information on upgrading to Cisco CallManager Release 3.3, 4.0, or 4.1, refer to the appropriate version of the Upgrading Cisco Unified CallManager document. You cannot upgrade directly from Cisco CallManager Release 3.2 or earlier to Cisco Unified CallManager Release 4.2.
For Cisco CallManager 3.3 Upgrades to 4.2(3)
If your server runs Cisco CallManager 3.3 and operating system version 2000.2.3 (or later), you can use the operating system upgrade CD-ROM or the operating system upgrade web download to upgrade the operating system to 2000.4.2sr10 or later.
From this good doc;
Hope this helps!
There is no specific feature comparion doc available which would point out the new feature between 3.3(5) and 4.2(3). You will have to check for New and Enhanced Feature of CM 4.0(2a) , then 4.1(2), 4.1(3), 4.2(1) and then finally 4.2(3) to get the complete list. Or contact ur cisco partner/SE/AM and check with them if they have any such document available.
Here are the main CCM 4.2 Feature Enhancments;
CISCO UNIFIED CALLMANAGER 4.2 ENHANCEMENTS
Directed Call Park
Log in/out of Hunt Groups
Call Forward on Non Registered or No Bandwidth
Cisco Unified CallManager Assistant on a phone
Cisco Communication Media Module
Department of Defense features
Cisco IOS? Software and Cisco Communication Media Module support for inbound Hookflash for Cisco Unified CallManager and Cisco Integrated Services Routers
Device mobility improvements (intra-cluster)
Complex passwords and password aging using Lightweight Directory Access Protocol (LDAP)
Call Pickup Notification (Audible/Visual)
Voice quality statistics
From this CCM 4.2.X guide;
Like Mahesh noted, there would be some other ones in CCM 4.1.3 etc. You can check the following link;
Hope this helps!