If you buy a fixed week you get the apartment what you see in always the same week. Fixed weeks have an assigned week and apartment number. No booking (with associated fee) is necessary but you are obliged to use every year the same week and apartment. If that is OK for you and the week is in a season you like, you will enjoy it.
The most preferred floor is 4th floor upwards, the top level is perfect. You should also be aware that apartments in different buildings may have different duration of sun shine according to their orientation to south.
Most prefer the high season autumn & winter from mid-October to end of March where you have in Gran Canaries a spring like comfortable climate and temperature with much sun and less rain – means the opposite you have at home. With children you might prefer the school holiday season. But you should be aware that week numbers are Anfi weeks, differ from calendar weeks, and may shift from one year to the other. The months with lowest demand are May and September.
If you have purchased a resale week you have the same rights as original weeks purchased directly from Anfi with the only exception that you cannot join with these weeks the Anfi Vacation Club (AVC, Anfi’s internal exchange club) or use an external exchange company as RCI. With original weeks bought directly from Anfi you can join the AVC (see here) and deposit and book your week on a yearly basis to be free in your time of usage.
Weeks you do not use yourself can be rented out, see private resales & rentals. You can even create your “own AVC”, renting out your week and renting another week. Renting out at high season is generally no problem, renting at low season not either.