Urd is probably the best starter out of that bunch easily.

Note: I rate starters based on how easily one can set up a team around them, and how far the leader can carry you in the game.

Ronia is a classic, but imo she's not that great of a starter since you... can't use her until you rank up quite a bit. And even then your team is gonna be rather shabby looking. Ronia teams only shine when rows are stacked; however as far as row teams go they're outclassed now. Still though, Ronia is solid all around.

Urd is simple. Her damage boost is 9-11x (one of the highest unconditional) and is color based, meaning it's very easy to build a team around at all stages of the game. Her off color LS means her teams can be both very tanky and easy to recover off as well. Her late game potential is also huge, though it is a bit REM focused: as her dream sub is Hino Kagut as well as additional Urds. Given the ease of using her early game and how powerful she can be late, I have to give her the best starter.

Isis is a very very good early roll, however she falls off late game. While her uevo does give her access to 20.25x, that's for all color matches. Ra can push x49, and Hathor gets similar damage and the same color bonuses but her LS activates 20.25x at 5/6 colors.

Bastet is another roll that can carry one far, and with the new Awoken uevo she looks better than ever. However she can be a bit rough to learn for new players, and her active isn't the best.

Meimei, or any Chinese god for that matter, is a solid starter roll. They'll carry most users pretty far, and pretty easy to learn. However, they also fall off late game, but they can be useful as subs.

Anubis is Anubis. Nuff said. If you've got the skills and luck you'll steamroll everything.

Sara and Andro sort of fall into the same problem area: they're both whale tier. Their potential is huge but your early game is going to suck unless you decide to throw your wallet at the REM during a water gala or something. Solid rolls, but can't recommend as starters.