BBM may or may not end up on other platforms. RIM has become really schizo and desperate as a company lately, so they're about as likely to put BBM on Android as they are to go out of business at this point. Basically, don't hold your breath on that.
When I say "push," what that means is that the e-mail goes through a server and is "pushed" to your device, rather than your device polling the server on a fixed schedule to "pull" the e-mail to your device. Push works very well with Gmail on Droid devices, but Blackberry's implementation of it is, IMO, still the best. The only thing I dislike about BlackBerry e-mail is that, at least on OS5 when I used it, it didn't display HTML properly and truncated messages. That doesn't happen on iOS or Android.
From what I know about the Torch, I know that the processor is underpowered, causing the phone to be sluggish. The other major complaint with the Blackberry is the lack of developer support (apps).
There is absolutely different tiers of devices. DO NOT go for the cheap Android devices. They're cheap for a reason. If you're going to spend money on a new phone, get some good hardware. Of course what phone you get will depend on what carrier you're with. If I were going to get a Droid, this would be my direction (this is completely opinion, but TW is a good person to ask as well).
Sprint: Nexus S - This is pure Android, no silly skins, no manufacturer nonsense. The Nexus line is Google's "vision" for what an Android phone should be.
Verizon: Droid Bionic - This one is pricey because it's new, but it takes advantage of Verizon's 4G LTE network. It's blazing fast, has top of the line internal components, and since it's the first in Verizon's second wave of LTE phones, it has some kinks worked out.
AT&T: Motorola Atrix 4G - Basically the same phone as the Bionic, only it came out about six months prior. The 4G refers to HSPA+, so it's not true 4G (at least not in the sense that LTE is), but it's still a very nice Android set.
T-Mobile: LOL, nobody uses T-Mobile. Unless you do, then I'd probably say MyTouch 4G or the Nexus S.