Early march, will be in a skiff but with no gunwale rod storage. So rods will just be laying on the deck. It would be preferred to have the 10 & 12 for the applications you stated above but this is not strictly a fly fishing trip so i cant justify bringing my whole arsenal. I am leaning toward the 12 for the reasons
@ifsteve stated.
Do you know where you will be? Like where are you launching and what rivers and area will you be targeting? In March, there are resident fish and what I've seen there over the years during March, they are not the big, big girls. More like 40-60ish and up to 80lbs If in the open bays or on the outside, then the 10 will work, but tough to man handle them in the deeper, swift currents of the rivers.
My advice will be to have the 10wt rigged and ready out on the deck. Capt Lemay's note is a good one, especially if you are bring a jon boat type of boat. I would also bring the 12wt still in the tube and reel stowed away somewhere, if you have the room, but not assembled.
For me, when I'm looking for poons down there, I'm basically stalking them like a hunter on foot. So I'll sit back from an area and watch it before I come on in to it. That gives me an idea if they are there or not, what they are doing, look to see if they are rolling, laying up, milling around or on the move. You can also get an idea of what size the fish are if you scope it out just right. That will also help you to know where and how you want to stage up the skiff.
You say I mentioned "Scope?" Yeah... sometimes I'll stay far enough away in larger areas to glass it with some binoculars to get more details on what I'm looking at, instead of just assuming what size it is and exactly what they are doing. That's not always the case, but looking far across an open bay or down around the corner looking down the river, it helps to glass it before I go in (especially with these eyes these days! I ain't getting any younger!

) and can assess the situation to see if I need to break out the big stick or not.

Believe me, with big rivers, a swift current and an intermediate sink line, it's no fun blind casting and lifting up line out of the water from a 12wt if I don't have to.
So when to break it out or not?? If I'm out in the open bays or on the outside, away from the river mouths and the fish are looking like they are pushing the 80lb mark, plus, then I'll break out the 12. Otherwise, I'm throwing a 10. If they look around 30-40lbs+/- or less, then I'm using my 9wt and if they appear under 20lbs, then I'll use the 8wt. I know you don't have an 11wt, but if you did, logic says it's somewhere in the middle, which it is, but try to not target fish over a buck twenty with that rod.
So in the rivers, it's a different story for me. With your 2 rods, if the fish are starting to look like they are 60lbs+, then I would grab the 12wt. That'll be the same at the mouth of the rivers. But in either case, if you approach each place or bend in the river to look down it before motoring to the next bend to check that stretch of river out, once you see bigger fish, just stop and very quietly break out that rod that you stowed, rig it up and get it all ready before you move on into the area. You can then stow one of your smaller rods and get it off the deck to make room for the 12. Then you'll have both of your big rods locked and loaded with your priority switching to focusing on your targeted poons rather than being distracted on other fish, kinda like a bird dog being distracted at the squirrels near by.

So tell yourself you are on a mission when targeting them and you'll be way more successful at it. And don't worry about the fish not being there long enough for you to get the other rod out and ready, cause they will still be there, as long as you don't make a bunch of noise doing so. In other words, they'll wait on you, as long as you don't spook them outta there.
Then with all the other general fishing around and scoping out areas for whatever will eat a fly, have the 12 stowed and your 10wt out on deck, just in case you see a mid size poon laid up and fining near the bushes.
That is my advise to have the best of both worlds, without carrying around both rods rigged and ready, all the time. If you only had to bring one rod, it would be a tough to make that call and really depends on the weather and how the weather has been over the past several weeks before you go down there. Also depends on if you are launching in Flamingo vs Choko. Also depends on water temps and when exactly in March. Too many vague variables to call that shot now. Fishing early in the month on weather trends that are somewhat cooler, then the bigger fish with still be south and offshore and you'll be dealing with more smaller resident fish, which are more 10wt size fish. If it's late in March and the weather was steady on a serious warming trend for 3wks+ after a more warmer late Feb (like if this weather keeps up being warm, from now on till your trip), it's possible that the bigger fish will push up from Florida Bay and offshore and come on in. Then you'll know what you need to do.
I hope this gives you food for thought.
Ted Haas