I'd suggest taking a look at our
Comprehensive iPod touch (Fourth-Generation) review.
The screen smudging issue is easily solved by applying a screen protector film, which you may want to do anyway. Prior to the iPhone 3GS with its oleophobic screen I used the Power Support Anti-Glare film on both my iPhones and I still use it on my iPod touch (they also make a clear "Crystal" version). Some of my colleagues here still swear by it even for the newer iPhone models, in fact.
As far as the RAM issue goes, you'll find that the extra room on the iPhone 4 is only a major concern for multitasking at this point -- running multiple apps and being able to "Fast App Switch" between them is a lot more comfortable on the iPhone 4. On the iPod touch 4G (and older iPhone models), you may find that apps are more likely to get shut down in the background if you haven't used them recently. This is not as big of an issue as it sounds, as any good app developer should build their app to deal with this properly and save state so you don't lose anything. In fact, this is the way ALL apps were expected to behave before iOS 4 added the ability for them to suspend to RAM.
It's also worth keeping in mind that the iPhone 4 is going to have more stuff happening in the background at any given time due to supporting the Phone and Messaging apps, engaging the GPS for Location Services and almost always having a 3G data connection to do things like check mail and receive Push Notifications. None of these processes consume huge amounts of RAM, but some are not there at all on the iPod touch and others are dormant except where you're connected to a Wi-Fi network.
Keep in mind that the iPhone 4 is considerably more expensive in terms of raw numbers, either by paying full price or committing to a contract with a cellular provider. That expense is frequently offset by the fact that you'd pay for a cellular contract
anyway, but it's still something worth keeping in mind.
The bottom line is that the iPod touch will always be the stepchild to the iPhone, which Apple seems to consider its flagship device. The iPod touch basically seems to have been designed for and targeted at people who either can't afford or don't want an iPhone for whatever reason. The iPhone has a better screen, better camera, more RAM, GPS/compass and an always-on data connection. The only advantage that the iPod touch has ever had over the same-era iPhone is its higher capacity -- you can get 64GB on an iPod touch while the iPhone caps out at 32GB, and Apple has always kept the iPod touch one notch ahead in capacity. Otherwise, the iPhone 4 is always the better choice if you can justify the price tag and need a phone.