You may want to choose a brushless motor which is usable in both your first fixed pitch helicopter and your second collective pitch helicopter. This is a little tricky but definitely possible if you plan wisely.
In the following section, 10-12T means 10 tooth to 12 tooth pinion. The lower tooth pinions are for duration, and the higher ones are for power.
There are three possible upgrade paths from the Corona: the ECO 8, the Eolo, and the Voyager E. All of these helicopters can use 3.17mm shaft motors in approximately the same Kv range as the Corona.
This requires choosing a 3.17mm shaft motor with a Kv of about 2400-2600. This results in a mild motor for the Corona, which becomes a power motor when moved to the ECO 8 on 10 cells. If you desire to use a Corona motor which will become a duration ECO 8 motor, then you will need a motor with a lower Kv (about 2200-2400) and use a larger tooth pinion on the Corona.
A motor with 3000 Kv is usable on an ECO 8 with 8 cells, but not really recommended for 10 cells.
Corona: 11-12T/8 cells
ECO 8 : 10T/8 cells
Corona: 12-13T/8 cells
ECO 8 : 12-14T/8 cells, 10-12T/10 cells)
Corona: 18T/8 cells
ECO 8: 17T/8 cells, 14T/10 cells
This requires choosing a 3.17mm shaft motor with a Kv of about 3300. This results in a power motor for both the Corona and the Eolo. The Mega 16/15/3 is fairly mild for both Corona and the Eolo.
This requires choosing a 3.17mm shaft motor with a Kv of about 3700. This results in a power motor for both the Corona and the Voyager. You must be careful to limit the throttle on the Corona because the maximum headspeed of 2000 will be exceeded if the throttle is not limited.