Intel's Core i3-8300 is a small step up from the Core i3-8100 that was released last year, during the first wave of Coffee Lake processors. Compared to the i3-8100, the i3-8300, which is $20 more costly, comes with 100 MHz higher clock frequency, 2 MB more cache, and a slightly faster IGP. We are not exactly sure about i3-8100 performance since we lack a sample, but the i3-8300 is certainly not 20% faster, which is what would be required to make both even from a price/performance perspective. The 100 MHz clock frequency increase is around 3%, and the cache will probably add another 3% performance on top of that for a total of 6%. Even if we are generous and assume 8%-10%, that's not nearly enough to make up for the $20 price increase over the i3-8100.

Against AMD's Ryzen 5 1400, the i3-8300 is the clear winner unless your applications are heavily multi-threaded, which they probably aren't if you are in the market for a $150 processor. Ryzen 5 1400 loses a significant portion of its more-cores advantage due to the low clock frequencies, which, paired with the lower IPC of Ryzen, have a fairly big effect on gaming performance and single-threaded applications like Microsoft Office and Internet browsing. If you feel your applications scale well with cores, then the better options could be the Ryzen 5 1500X ($160) and Ryzen 5 1600 ($190).

The Intel Core i3-8350K is an interesting SKU because it allows multiplier-based overclocking, which isn't possible on any of the non-K Intel processors. Just paying $30 more than the i3-8300 won't do the trick though since you also must have a Z370 motherboard as Intel has disabled overclocking on motherboards using cheaper chipsets. So that's around a $60 overclocker's tax, which, after overclocking the 8350K, should give you around 20% extra performance over what the i3-8300 offers—so it is not really worth it unless you enjoy overclocking a lot. The Ryzen 5 1400, like every other Ryzen part, features unlocked multipliers, and AMD supports CPU overclocking on even its mid-tier B350 chipset.

Unlike most AMD Ryzen processors, the i3-8300 (and all other Intel processors) comes with integrated graphics, which is a cost saver for systems that are focused on productivity, Internet browsing, and possibly even casual gaming. Building a media PC using Intel Integrated Graphics also works reasonably well. Should you want more gaming performance, then AMD's Ryzen APUs with integrated graphics could be an alternative. Their integrated graphics are about 3x as fast as what Intel offers, roughly on the levels of the NVIDIA GT 1030/AMD RX 550. While that certainly won't give you 4K gaming, visual fidelity and FPS in games do noticeably improve. The Ryzen APUs are based on AMD's 2nd generation Zen architecture, which have higher IPC and higher clock speeds—a noticeable difference over 1st generation Ryzens, which helps them stay competitive with the i3-8300. At slightly higher pricing, the Ryzen 5 2400G is a solid alternative to the i3-8300 if you want to use integrated graphics exclusively. If you plan on getting a dedicated mid-range graphics card (GTX 1060 and above), I'd probably not waste money on an IGP that's never used and stick with Intel for higher gaming performance.

Last but not the least, we have the Intel Core i5-8400, which is quite a bit more expensive than the Core i3-8300 ($35), but offers six physical cores that improve performance a good deal, especially in games, when paired with a high-end graphics cards (GTX 1070 Ti and above). With the i5-8400, you begin to enter Intel's price-performance sweet spot. This chip won't bottleneck high-end graphics cards, and its 6 physical cores will provide a good degree of future-proofing.

The Core i3-8300 is a very decent processor that will do fine in all consumer workloads, but it is under attack from all sides. If you want better price/performance, the i3-8100 will give you more bang for the buck at slightly lower performance. If you want better integrated graphics, then AMD Ryzen APUs offer much higher IGP performance. Should you be looking for more multi-threaded performance, then the Ryzen 5 1400 and 1500X with their SMT and unlocked multipliers have you covered.