dnd 5e – Should I do a multiclass as a rogue fighter, or take the double bearer dowry?

I can not decide which route would be best for me to take the fourth level; He could take the double-bearer dowry or he could be multi-class in a fighter by a few levels.

Here are my statistics:
STR 15
DEX 20
WITH 15
INT 16
WIS 12
CHA 16

I have a high level high level rogue, a swashbuckler archetype and high statistics. I have two short swords today, but I would love to pick up two rapier for the larger die.

The feat would help my CA (currently in 17 with studded leather armor) and allow me to have the rapier.

Multiclassing for three levels of fighter would give me the style of fighting with two weapons (adding my modifier to my second attack would help my RPD), some higher impact dice, second breath, a surge of action (which is not that deadly anymore that I can only sneak once per round, but the damage of the modifier is pretty good), and a martial archetype (I'm thinking of Monster Hunter for superiority dice and the release of rituals to detect magic and protection against good and wrong).

But, the multiple classes also diminish my rudeness, and the furtive attack is really what I have in my favor, so stopping this development makes me stop.

Do you have any opinion? It could be multi-class and then, for my next rogue level, take the dual bearer dowry, I do not know if that's better.