One of the main differences in Pesukei D’zimra between Nusach Sefard and Nusach Ashkenaz is the placement of Hodu. In Ashkenaz, it comes after Baruch Sh’amar while Sefard has it immediately after the karbanos and before Baruch Sh’amar. Hodu used to be recited when karbanos were offered in the Beis HaMikdash, therefore, Nusach Sefard places it immediately next to the karbanos we recite today. According to Nusach Ashkenaz, Hodu is full of verses of praise and therefore should be part of Pesukei D’zimra. Therefore, Ashkenaz first recites Baruch Sh’amar to begin Pesukei D’zimra. Both Nusach have good reasons for why they place Hodu where they do and a person should follow his custom.