Mixing bowls, even those that are designed with little spouts on the sides, are not really made for pouring. Liquids tend to overrun the tiny spout when pouring, and dry ingredients also need a lot more direction than the design can offer. For liquids and batters, a measuring cup with a more defined spout tends to be the best option. For dry ingredients, I find that using a pouring shield helps with a stand mixer, and that a large, flexible cutting board is great for sifting and directing ingredients into a particular bowl. I just recently saw this Large Flexible Mixing Bowl and realized that it can do the job for both dry and liquid ingredients with ease.
The large 2-qt bowl is made of silicone and can be bent and pinched to any angle, creating a small or narrow spout that will funnel flour into a stand mixer or drizzle milk and eggs into a cake batter. In addition to being freezer and microwave safe, it is heat resistant to 490F, so you can even transfer a hot mixture into it right from the stove (which would come in handy if you were tempering eggs for a custard and don’t want to handle a heavy, hot pot while you work!). This is one of the first large silicone bowls I’ve seen and, compared to all the little silicone “prep” bowls out there, it is probably the only one that seems useful enough – as it does a job that standard mixing bowls can’t do – I’d want to have it in my kitchen