[Captivate General] jekyoo_style:
Screen: The retina display is slightly better than the super amoled. I ran both side by side running the same movie and you can definitely that the captivate has a saturated color hue. The colors didn't look natural compared to the iPhone 4's retina display. Two things that I liked about the Captivate is the display size and the black. IMO, the 4.0" display is the best size display for a mobile phone. 3.5" is too small and 4.3" is too big. Because of how the super amoled screen is made, black looks black. On the retina display, it's a faded black due to the backlight. You can't go wrong with both, it's a win-win.

Performance: On paper, the Captivate is much faster but it doesn't feel that way. But, I'm sure this will change once a vanilla froyo or CM6 is cooked up for the Captivate. One of the things I miss most about my Nexus One is the vanilla OS. Samsung's touchwiz is literally killing the phone. It's ugly and sluggish.

Antenna problem: I don't know if it's just me but the Captivate has a worse antenna problem than the iPhone 4! When I'm doing the death grip on the iPhone 4, at most, I get a 2 bar signal drop. For the Captivate (using my right hand), the Captivate completely drops 0 bars!

Battery life: From my real life experience, the iPhone 4 has bettery battery life. I have less than 10% battery life on my Captivate while my iPhone 4 is holding strong with 40-50%. This maybe because of multitasking since the iPhone 4 does not have a legit multitasking system and lacks good push notifications. Once a jailbreak is available for the iPhone 4, I will install backgrounder (a true multitasking app) and see how well the battery life stacks up then.

Browsing: When uploading websites, the Captivate beats the iPhone 4 by a very small margin. Probably 2-4 seconds difference. Also the fact that the Captivate has flash is an instant win.

Design/Built: iPhone 4 looks better, sturdy and the build quality is phenomenal. The Captivate feels cheap because of the plastic. This is one of the main things I dislike about the Captivate. I wish the exterior was a metal build.

Typing: 1) If the Captivate had a multi-touch keyboard, it would definitely be the best keyboard. 2) If the iPhone had a legit user dictionary, it would have the best keyboard. Both are great but are lacking a feature that the other hands. I give the edge to the Captivate since you can choose which keyboard you want to use.

iOS 4 vs. Android 2.1: I'm not even gonna address this just because this topic has been beaten to death. Both have their pros and cons and I feel like you can't go wrong with either. It's all down to personal preference since 1 is lacking what the other has imo. If iOS and Android had a better, it would be the best OS ever (lol). A lot of the "problems" with both phones can easily be fixed with a custom rom or jailbreaking.

As for your question:

Android definitely handles emails better than iOS. It's one of the things I love about Android. Emails are pushed instantly to your phone while as the iPhone, it can take 10-20 mins for you to get it. If you use a lot of google products like calender, gchat and gmail, Android is for you. It's so integrated, I love it.