I have done it three times, I would say deck 8 and port side, midship. Deck5 and above a great.
Whilst you can go into any lock, the port side has had great views of the land, the railway, some buildings, the starboard side is good but mostly just land.
Now there are new locks opening, but I will would say port martini ally has it.
It's a very very long day, you would have to be up on deck very very early to try to snag a place to view on deck, as the cruisers were staking out thier places from 5 am on our cruises.
In a verandah you are protected from the sun, your near the equator there so very powerful, even if it's cloudy you get burnt. You also get protected from the tropical rain storms that come in fast. This water supplies the canal and locks and gates and lakes so you can see how much comes down.
On deck you can get sunburnt, wet from heavy rain, and loose your place if you go to the restroom, or lunch. In your own room you can call room service, the kids can watch a movie you can refresh with aircon inside, and still walk the ship, see both sides, eat the lunch BBQ and come face to your space in the shade.
Ships photography took photos of us on our verandah as we waved to them, they were on the walls on the locks.
Lower decks can just get views of walls either side in the deep loves until the water brings the ship up.
The Panama day is long, often starting around 6 am and lasting to 6 pm, it's a port adventure in itself, enjoy it on your verandah, and gave the best of everything, being able to walk the ship and gave your own space and no need to join the " Disney parade" style stakeout of some space on deck in the crowds and have everyone close by in your photos.