This is an easy one. If you are willing to spend $1,000 and/or are used to always buying the Pro model then hold out for the Pixel 9 Pro. If you have no desire to spend that much and would prefer "best bang for the buck", but the Pixel 8a, you won't be disappointed.
With the deals and good trade-in values, the Pixel 8a will be incredibly affordable so if price and value are important to you, go 8a.
But if you are like me and always make use of the premium features and can rationalize the price difference, hold out for the 9 or 9 Pro.
Keep in mind, when the 9 is released, Figure will likely provide really good trade-in values which can help with your purchase. For example, I got $400 back on my trade-in of my Pixel 6 Pro when I bought my Pixel 8 Pro and Google was giving out a FREE Pixel Watch 2 so it was worth it to me.