Ephraim: Which Siegmund?

There have been at least 2 other posts, which are on the same page in the forum here (so you could have spared yourself some time and actually looked a bit), that deal with this exact topic and give the required details. I'm just gonna give you the links instead:

https://fireemblem.gamepress.gg/q-a/which-refine-hp-spd-regular-ephraim

https://fireemblem.gamepress.gg/q-a/ephraim-teamplayer-or-solo-monster