When mixing and matching, the primary concern, of course, is for how components work with one another based on the sound one is looking for, e.g., how much detail versus, say, long-period listenability (although I think such trade-offs are slowly shrinking thanks to evolving technologies). Although differences between tube and SS amplification are narrowing at higher price points, substantial differences persist in lower-priced equipment. But that's largely a matter of personal sound preference and whether one wants to plug it in and forget about it or have the option of tube rolling (IMO, that way madness lies).
The next consideration, for me, is the performance-for-price ratio, given the budget constraint. We all want to get the biggest bang for whatever bucks we spend. Suppose the overall budget is $5000, and I've already bought speakers and a source for $3000. So, I have $2000 left for amplification. I want to spend that $2000 on equipment that has a strong reputation for performance (e.g., providing 80-90% of what I'd get if my budget were two or three times greater), reliability, customer service, and to a lesser extent visual aesthetics. If much overall budget was $10K instead of $5K, the same considerations would apply.
In choosing components, I don't restrict myself to specific manufacturers, but I have found, over time, that I tend to go with certain manufacturers over others based on the considerations I have described. In my (inevitably) limited experience, I have found that some companies like Rega, Parasound, and Tekton consistently provide high performance-for-price value. I also have gotten good value for my money from Mytek DACs, although, now that manufacturing has moved from Poland to the US, their prices are inevitably rising. Many audiophiles, no doubt, would consider my choices boring or too obvious but, as with all things audio, de gustibus non est disputandum.