[myTouch 4G Q&A, Help & Troubleshooting] RealityDesign:
I currently own both. Deciding right now which one to send back. It's looking more and more like it will be my G2. Here's my opinion after owning both:

I slightly prefer how the G2 looks. It's a classier phone. Part of that class is the all metal feel, and the soft buttons. I wish the myTouch didn't have this cheap looking chrome around the bezel. If it was like a piano black or even just flat black like the rest of the phone it would be much better looking. The plastic hard buttons are obviously not as nice as the soft buttons on the G2. That said, it's not really a deal breaker.

In your hand, and in your pocket, the myTouch wins. It's thinner, lighter, and I personally think it just feels better. The G2 was a little clunky for my tastes, but still acceptable.

The screen is basically a tie for me. They are the same resolution, and the myTouch is 0.1" bigger. The net result is that if you really scrutinize the two phones, the G2 is going to look ever so marginally sharper. Obviously this is because it has a slightly smaller screen with the same resolution, or more pixel density. In reality, unless you did a side by side caparison and stared at both of them, they are the same. Interestingly enough, when comparing the two, I found the color accuracy to be better on the myTouch, and it was slightly more vibrant. Again, they are so close this is a tie.

After having the G2 for 3 weeks, I've used the physical keyboard twice. Clearly, I don't have a use for it. This alone is the reason to get a G2 or not, in my opinion. If you don't use the keyboard, the G2 is just a bulkier, heavier myTouch with the possibility of hinge problems in the future. If you do use it though, the added weight and thickness is well worth it.

Stock for stock, the myTouch is a faster phone. However, for anyone on this forum, that's completely irrelevant, because you're just going to download visionary and vision_oc.ko and overlock your G2. When both phones are rooted (or temp rooted) the performance is basically identical. The G2 was just underclocked from the factory, presumably for battery life.

The only other things that set the myTouch apart from the G2 are the front facing camera, metal contacts on the side for a dock, and HTC sense. The front facing camera is cool, I don't know if I'll ever really use it. It's nice to know I can if I want though. Being able to use a dock is nice, although I don't know if I'll ever even buy one. HTC sense, in my opinion, is crap. However, some people really like it, and this can be a bonus for them. For me, I just use launcher pro anyway, so whether the phone has sense or not, it operates identically. I've actually found with the myTouch that the combination of HTC sense and launcher pro is actually kind of nice.

Last but not least, the genius button. At first, this seemed like a gimmick, but it's actually become one of the reasons I may end up keeping this over the G2. I'll illustrate the power of this little button for you. On both phones, this is how you would send a text message by voice:

G2: Press and hold the search button. Say, "Text John Smith." The text message window appears. You tap the message body, then tap the microphone button. Then you say, "This is a test message." Then you read your message and make sure it looks right. Then you tap send.

myTouch: Press the genius button. Say, "Send text to John Smith." The text message window appears, and a voice asks, "Would you like to dictate?" You say, "Yes." It prompts you to speak, and you say, "This is a test message." It then says, "This is a test message. Would you like to send this message?" You say, "Yes."

On G2, you had to look at your phone 3 different times, read your text message, and press several buttons. On the myTouch, you never looked at your phone, and pressed one button. Obviously if you want to text and drive, the myTouch is the phone for you.

So after all that, did I really sway you one way or the other? Probably not...lol. They are both good phones.

tl;dr

If you use a physical keyboard, get a G2. If you don't, get a myTouch. If you're on the fence, try out the genius button, it may sway your decision.