Additionally it’s important to look at how the ETFs work. I believe the ETFs in question here are LQD and HYG for investment grade and high yield respectively. These ETFs track the iboxx indicies for IG and HY. Even if the Fed is buying BlackRocks ETF, this bolsters the prices of the individual bonds, which then moves indices higher, thereby also moving up other provider’s ETFs along with the entire fixed income market. Given this is the case, one should pick the most liquid ETF for each asset class (Ideally all ETFs should be purchased weighted by the NAV or trading volume of each ETF), in that case it would be BlackRocks for US fixed income.