I find it amusing that naval infrastructure is sitting at 4 largely because many people find it "niche" or won't use harbors in every game, and certain favorable conditions need to be met. Retinues is currently sitting at 12. I have never done a bombard or musket timing push. Rarely do I even seek to conquer any cities. I don't know how many bombards people need, but I would think 1-2 are more than enough to break down city walls in conjunction with a supporting army. By the time bombards are available, niter should have already been unlocked and improved, and I'd have enough for as many bombards as I need/want. If i had no niter at all, I don't think buying it would be worthwhile, as I find AI wants a steep price for it. If I wanted to do a niter unit rush, I don't think this card would much help, not that I ever would. As for warriors into swords, again, I feel the timing is off from unit to card unlock, and I don't know if I ever had a situation where this card has been or would have been helpful.
Those persons who feel differently from me, I don't think they are "wrong," but that we play the game quite differently. Therefore, we are both right from our own perspectives. Another example of why these elimination games carry a grain of salt.
However, I do feel that naval infrastructure, as aptly detailed by @kyrat, is both "wider" and "stronger". That is to say it has more universal benefits (more games, more playstyles) and stronger effects (gold, production, science) and is attached to a district that itself has multiple roles (much like holy sites, imo).
(I used to play mainly pangea, but recently have favored continents. On continents, I rarely find myself far from water. Naval gameplay has been surprisingly refreshing as of late.)
Thus, I shall vote exactly the same as Kyrat: Retinue down and naval infrastructure up.
Naval Infrastructure (5)
Professional Army (33)
Retinues (6) (9-3)
Edit: There was a score correction at the same time I posted. My numbers should be correct now.