http://msdn.microsoft.com/en-us/library/8z6watww.aspx
Based on the above link what should i chose ? I am forced to stick to .Net 3.5 because it has less hardware requirements.. However on my XP 2gb ram machine it takes 30 s to load a .net 3.5 program..,so i think that it would take hours to run a simple .net program at machine with less than 512 mb ram !! so there is no reason to stick to 3.5..
But it takes too much disk space!! WTF 1.5 GB for .net 4 ??? it is too much..
What should i choose for better compatibility ?
Chances are your application will be able to target the .NET 4.0 Client Profile. Disk Space requirement is 600MB, however the download size for your users (IIRC) is around 40MB.
I see no reason to use 3.5 over 4.0, the benefits definitely outweigh the negatives you could find about it.