I ran external for awhile with my reeflo hammerhead and I much prefer submersible. It's just much quieter and takes up less room under my sump. If I ever had a dedicated tank room with all the equipment in it, I would happily go back to external as the noise or space would not be an issue.
Another factor to think about is the relative efficiency of the newer DC pumps these days. The amount of wattage used to drive those pumps are just a fraction of the old Reeflo pumps.
I'm a big fan of my Jaebo DCS12000. I'd buy another one in heartbeat. Quiet, efficient, controllable, and plug n' play. I have an extra in case it sputters out on me. At $120 compared to the other pumps out there, it's practically disposable for something that moves 3,200 GPH.
To plug my external hole, I just used a PVC end cap that fit the bulkhead. I used a bit of silicone and then just twisted it on there... done!