Checklist every time. Then you know you won't miss/haven't missed something if your checks are interrupted, when the workload is high etc etc. Also if it is your IRT and your examiner says words along the line of "you can do checks from memory or a checklist, but if you do them from memory and get them wrong it is a fail item" (or words to that effect, but it is big hint) you give him one less chance to make you spend even more money. Just try to avoid falling into the trap of becoming 'checklist driven' and endlessly covering the same stuff instead of doing a relevant set of checks when airmanship dictates.