It would be more efficient from a memory standpoint to concatenate the strings in the front. However, you will be using CPU doing it in the front end. The decision is a trade off.
1. If you are displaying the combined string frequently, it makes sense to do the concatenate in the script -- if you hacve available RAM. .
2. If you are displaying the string infrequently, it makes sense to reclaim the RAM in exchange for an occasional use of CPU.