Jeanne or Martha ruler?

Martha is a offensive ruler(funny as that sounds) while Jeanne is a support/tank so generally whichever role you need more as both are excellent at their roles.

Obviously Martha is much easier to get due to being a 4* and if you want the CEs that means the summer banner will almost guarantee getting at least something you want. All in all they fill totally different roles from a gameplay perspective so it mostly comes down to who you like more.

First off jeanne has a niche of being able to clear certain challenge quests later on after her NP gets an interlude and her skills will benefit her more as majority of them are sevant based. Ruler Martha is more standard buster crit with the benefit of the ruler class advantage.
If you like Da Vinci and Jeanne by all means roll since she they have their own niche and will always be useful. Only recommending this since it seems you already have a decent team and youre simply rolling for the characters you like. Otherwise summer servants the way to go. The 4 stars are excellent and wayyy easier to get.

I'm going to assume you're not a whale and say that rolling the summer banner for Martha will more likely produce a favorable outcome. Hindsight is 20/20, so if you get jeanne or davinci, you made the right choice. But the gacha is made to punish you and tempt spending so it always feels bad to go hard on a banner, only to fail.

Martha is a nice get. Easier to obtain being a 4 star. Jeanne shares a rate up with jack in the next paid gacha, so your chance of getting her then will be 50%.

Rulers are nice, but by no means a must. They're great for certain fights, but day to day content can be more efficiently cleared with class advantage.