Disclaimer: I'm biases for Android and against iProducts. I'll try to be as objective as I can comparing the two though.
Sid, you're just going to be buying the phone outright? Make sure Straighttalk will work with the Galaxy S4 (and prepare yourself for the sticker shock). And FYI, the American market gets a slightly different version than the European market, which gets the 8 core Exynos (clocked at 1.6GHz). The Americas get a quad core Snapdragon clocked at 1.9GHz (nothing to sneeze at). The European S4 scores better in benchmark tests, but not so much that it's worth worrying about - the American S4 beats pretty much anything else out there. Plus, the European version doesn't support 4G LTE. Straighttalk uses existing networks from Verizon or Sprint (CDMA) or TMobile or AT&T (GSM). There shouldn't be any problem using an unlocked S4 you bought off Amazon or from Bestbuy with Straighttalk.
There's some big difference between the S4 and iPhone 5.
Most obvious, as far as having it on you every day, is the size. The S4 is a large phone (although ever-so-slightly smaller than the S3) with a big screen. The iPhone 5 takes up way less pocket space. Obviously this is because of the screen sizes. I wouldn't call the screen on the iPhone 5 "cramped", but it definitely gives you less to work with. And if you want to put some movies on your phone to entertain yourself while traveling, the larger, more detailed screen of the S4 is the obvious winner. If I were you I'd pop into a cell phone store (the 4 major carriers all offer both the Galaxy and iPhones) and see which you'd rather put in your pocket (or clip to your belt). If the large size isn't an issue, the S4 wins hands down for its screen. Especially if you want it to perhaps replace a laptop.
Also obvious is the OS. iPhones are simple and easy to use. The trade-off is that they're not even remotely as customizable as Androids are. Conversely, Androids have a steeper learning curve because there's so much more you're able to do with them. In this regard, there really isn't a "right" or "wrong" regarding a person's preference. I can't fault an iPhone user for preferring because it's simpler. Many people these days don't even want smart phones, they just want to make calls. It all comes down to how much you're wanting to do and how much you like to customize.
The S4 has a larger battery, longer battery life on that battery, and the battery is replaceable so you can keep a charged spare (or 2) handy if need be. Very good to have while traveling. The S4 also uses a plain-ol' micro USB to charge. No need for a proprietary connector.
The S4 gives you more value for your money. Higher res screen, higher performance hardware, and you're not paying out the nose for storage space like you do with an iProduct. A 16gb iPhone 5 will run you $720-750 off-contract, with another $100 or so for each jump in storate (32 or 64gb). That's just insane. I ordered a 64gb class 10 microSD card off Amazon this afternoon for $55. Apple's math don't add up. For less than the price of a 16gb iP5 you can get a 16gb S4 and a 64gb microSD card. If you need more than that (and I can't imagine you would), there's a 32 and 64gb version of the S4 coming out as well.
One other thing to heavily consider is
this app for Android phones. For $8 it combines FoxFi and PdaNet. FoxFi works as a wi-fi hotspot and Bluetooth tethering, and PdaNet does wired tethering. There might be issues with using FoxFi's wi-fi hotspot and the 4.2 Jelly Bean on the S4, but Bluetooth should work fine (if your laptop supports it - if not, you can buy a dongle for cheap). Or just use the wired tethering with PdaNet, which is often the better choice anyway, since either way, providing internet for your computer sucks down the phone's battery. The best part is that it's only $8,
once. No $20/month (or more) extra for data you're already paying for. For obvious reasons, carriers, especially ones that offer unlimited data, do their best to block use of these (and similar) apps, but there's almost always a way around them. But if you're buying an unlocked phone, there shouldn't' be any problems at all. In any case, you can download the demo for free and see what works or doesn't. The $8 full version unlocker gives you unlimited use, whereas the demo times-out after a while and needs to be restarted.
Or you could root your phone, and do all the tethering/hotspot stuff for absolutely free (plus a bunch of other neat stuff), but this voids your warranty, and messing around with root access with your Android isn't for the timid or uninitiated (
trust me).