Generally speaking it's good to carry a few different plugs especially with a new engine, if you give a few more details I will do my best to help.
1. New or used engine
2. If new has it been broken in and given a good base tune
3. Ambient temp and elevation of usual track or spot you drive it at.
4. What kind of driving (race,bash, or wide open throttle for long stretch)
5.What kind of load will it be under(make and model of vehicle) some vehicles bear a greater load than others
Also what are your objectives (maximum performance or longevity of engine parts. With these things in mind I'm sure we can get you in the ball park. Rule of thumb is hotter environment colder plug , higher nitro% colder plug. Another thing to consider is when an engine gets hotter it runs leaner, now depending on your tune this could be good or bad.
FYI, here in Hawaii in the summer at 3,500ft elevation an average day is between 80℉-90℉. In a race situation but also not being sponsored(no free engines for me), I want performance but also don't want to cause unnecessary wear. I run a plus 21-4bttwc with 30% O'Donnell, in an old inferno MP7.5. With this in mind plugs I carry: CTO6,CTO7.or equivalent, these will get me through the summer to mid fall