Do I buy a laptop with a higher clock speed 2.x and 3r generation intel processor or 4th generation and a much lower speed 1.6-1.7? since laptops with these processors are in the same price range
And is there a notable difference between xxxxu and xxxxm processors? (4300u and 4300m)
Older processors may have higher clock speeds in laptops but they produce more heat and usually have only one core. Newer processors would produce less heat and have multiple cores, which I personally prefer. Multiple cores on a processor is basically one microprocessor divided into multiple. Different cores can be performing their own calculations instead of relying on one.
Newer processors also have larger caches, which is their memory. The cache is used in repetitive situations, such as when an equation is repeatedly calculated with only minor changes, the cache will remember previous parts of the equation and produce more efficient, fast answers. So newer personally is better, but you should look into the processor specifications still, because there is much more that just frequency that makes one good.