Installing fresh Linux server - 32 or 64bit - which version do you prefer and why?

you have to make your decision taking into account , among others your h/w setup.
If for example you have more than4 GB ram then using32bit is useless, go for64 bit.
Few years, ago i would say that64bit version would be problematic due to the fact that there were not stable releases for updates and system was crashing or needed reinstallation.
Now, I am using centos64bit with16 GB ram (for a heavily working server) and have no problems what so ever running24/7.
If you have written code for32bit and want to move it to64 bit system you might have to make adjustments.

you can install red hat5.4 or5.864 bit server because we are using5.8 linux server in our data center for last2 years and its running fine.
Use Data Protector or paragon or netbackup for your whole os image backup for safety

If you have server with over4 GB ram I recommend64 bit and if you ask me which distributor I recommend centos because it's stable with me over3 years

you have to make your decision taking into account , among others your h/w setup.
If for example you have more than4 GB ram then using32bit is useless, go for64 bit.
Few years, ago i would say that64bit version would be problematic due to the fact that there were not stable releases for updates and system was crashing or needed reinstallation.
Now, I am using centos64bit with16 GB ram (for a heavily working server) and have no problems what so ever running24/7.
If you have written code for32bit and want to move it to64 bit system you might have to make adjustments.
hope this helps

64 has more performance ..
and allow you to use all of your RAM ..
beside as all ay above .
you can use it with RAM more than4G ..
and when the RAM >4G the expect will be less than64

It depends on your requirement, for example if you require your server to be a KVM server on RHEL6, then you should go with64-bit as KVM only operate on64-bit systems.
Another example if you are going to run Oracle and you need8 gigs of RAM, then you should go with64-bit, because32-bit will only support maximum4 gigs of RAM.
Decision is taken from requirement analysis.