There are two major processor vendors on the market today, Intel and AMD. It is generally accepted that for poker the best choice is Intel, as it is faster. However, this is an eternal dispute like MARVEL or DC. AMD processors have a nuance - they heat up more strongly, so a standard cooler may not be enough. Personally, I have an Intel Core i3-6100 3.7GHz, worth $140. After choosing a processor, look at its Socket. You need to choose a motherboard with exactly the same parameter. Budget "mother" is enough. But when choosing, make sure that it has outputs for your monitors and that it supports the DDR III memory type.