Measurements and weight:
Samsung Galaxy S4: 137x70x7.9 mm, 130g
Apple iPhone 5: Apple's iPhone 5 is one of the slimmest and most lightweight smartphones on the market. It features a design that is a mere 7.6mm thin and weighs only 112 grams. Rumors suggest that the iPhone 5S will keep the same design as the iPhone 5 which means that it could keep these measurements as well. It's undeniable the upcoming Apple iPhone5S is lighter and more small-hand friendly than the Samsung Galaxy S4.
Display:
Samsung Galaxy S4: 5-inch full HD super Amoled 1920x1080 display, 441 ppi
Apple iPhone 5S: Phone 5S will have a higher-resolution display than the iPhone 5, potentially based on the new IGZO (Indium Gallium Zinc Oxide) material. But whether iPhone 5S will compete with the new released Samsung Galaxy S4 is still a question.
Processor:
Samsung Galaxy S4: 1.6 GHz octa-core processor
Apple iPhone 5S: The iPhone 5 uses an A6 chip, while the iPad 4 has a more advanced A6x chip. Apple's iPhone 5S is may step up to use this more advanced chip architecture. And we think the eight-core processor in the Galaxy S4 could be overkill.
Samsung Galaxy S4: 2,600 mAh
Apple iPhone 5: The iPhone 5 does not feature a removable back which likely means that iPhone 5S owners will be stuck with the battery. The Galaxy S4's battery seems significantly bigger than the upcoming iPhone 5S's.
Software:
Samsung Galaxy S4: Android 4.2.2 Jelly Bean
Apple iPhone 5S: While the iPhone 5 ushered in the era of iOS 6 with Apple Maps, Passbook and more, the iPhone 5S will more than likely arrive with the new iOS 7 on board. But I think picking which operating system is better is largely down to the individual user's personal preference as each of the two operating systems has its unique and innovative features.
Camera:
Samsung Galaxy S4: 13MP rear, 2MP front
Apple iPhone 5S: Camera in the upcoming iPhone 5S is rumoured to be capable of taking "Super HD" pictures. In order to take snaps at that resolution it'll need to have at least a 13 mega-pixel camera.
Storage:
Samsung Galaxy S4: 16/32/64GB user memory + microSD slot (up to 64GB)
Apple iPhone 5S: 16/32/64GB internal
Both devices are available with multiple storage options. If you really want to store a lot of media, Samsung is offering up its new HomeSync product, which offers users 1TB of storage via a streaming server.
Connectivity:
Samsung Galaxy S4: GSM/GPRS/EDGE/HSPA+/4G LTE Cat 3; Wi-Fi 802.11 a/b/g/n/ac, GPS, NFC, Bluetooth 4
Apple iPhone 5S: GSM/EDGE/HSPA+/HSDPA/LTE 4G; 802.11a/b/g/n Wi-Fi, 802.11n on 2.4GHz and 5GHz; Bluetooth 4; GPS
The upload and download of either device will depend on the network carrier and location of the user.
Overall:
However, I think specs aren't always 100 percent accurate, which means it is impossible to know which is better till we've had more hands-on time with the iPhone 5S. Certainly the iPhone 5S is one of the S4's biggest potential competitor, its real enemy, which will appear in the second quarter of the year.