SQL> create table t4 as select * from t1;

Table created.

SQL> create table t5 as select * from t1 where 1=2;

Table created.

SQL> create index i5 on t5(id);

Index created.

SQL> select bytes,extents,blocks from user_segments where segment_name='I5';

     BYTES    EXTENTS     BLOCKS
---------- ---------- ----------
     65536          1          8

SQL> alter index i5 unusable;

Index altered.

SQL> alter table t5 nologging;

Table altered.

SQL> Alter session set skip_unusable_indexes=True;

Session altered.

SQL>  insert /*+ append */ into t5 select * from t1;

563904 rows created.

SQL> commit;

Commit complete.

create index i4 on t4(id);
Vs
alter index i5 rebuild online;

create index i4 on t4(id)


call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        1      0.00       0.00          0          1          0           0
Execute      1      1.17       3.38       9497       7869        335           0
Fetch        0      0.00       0.00          0          0          0           0
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total        2      1.17       3.38       9497       7870        335           0

Misses in library cache during parse: 1
Optimizer goal: CHOOSE
Parsing user id: 5

Elapsed times include waiting on following events:
  Event waited on                             Times   Max. Wait  Total Waited
  ----------------------------------------   Waited  ----------  ------------
  db file scattered read                        257        0.00          0.34
  direct path write                               4        0.00          0.00
  direct path read                               25        0.00          0.00
  log buffer space                               57        0.15          1.71
  log file sync                                   1        0.00          0.00
  SQL*Net message to client                       1        0.00          0.00
  SQL*Net message from client                     1       36.57         36.57
********************************************************************************

alter index i5 rebuild online


call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        1      0.00       0.02          0         21          1           0
Execute      1      0.94       2.88       9558       7889        445           0
Fetch        0      0.00       0.00          0          0          0           0
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total        2      0.95       2.91       9558       7910        446           0

Misses in library cache during parse: 1
Optimizer goal: CHOOSE
Parsing user id: 5

Elapsed times include waiting on following events:
  Event waited on                             Times   Max. Wait  Total Waited
  ----------------------------------------   Waited  ----------  ------------
  db file sequential read                        61        0.01          0.01
  db file scattered read                        257        0.00          0.10
  direct path write                               4        0.00          0.00
  direct path read                               19        0.00          0.00
  log buffer space                               54        0.15          1.39
  rdbms ipc reply                                 2        0.04          0.05
  log file sync                                   1        0.00          0.00
  SQL*Net message to client                       1        0.00          0.00
  SQL*Net message from client                     1        2.45          2.45
********************************************************************************

Anyway, I would favour the rebuild (as it will reuse the index definition).