normally the scripts will sugest a table rebuild (create temp, copy to temp, drop original, rename temp, rebuild indexes) if it thinks this will be faster than an alter table. This will often be down to how many indexes you have and what effect on these will be with the table redesign, especially if you have inserted columns into the middle of the table as it will have to re-page all of the existing data.
normally the scripts will sugest a table rebuild (create temp, copy to temp, drop original, rename temp, rebuild indexes) if it thinks this will be faster than an alter table. This will often be down to how many indexes you have and what effect on these will be with the table redesign, especially if you have inserted columns into the middle of the table as it will have to re-page all of the existing data.