I might say MacBook Pro. However, first, I say wait a month. I believe we will get updates to all the Mac notebooks in June. So, it's worth the wait.
The MBA is so much more portable. It is so light, it's so small, it's display (without lines) is so beautiful. It takes up the space of a few magazines in a bag. It is better in an airline seat, and it is all about fun.
However, if you need more RAM, more screen real estate, an optical drive and more power, the MBP is a great Mac. The unibody build is incredible.
The thing right now, is that both are nearly seven months old. So you are paying full price for seven month old technology. Apple normally updates its Mac notebooks every six months, so a June update is very possible.
There has been a rumor about an OLED display in Mac notebooks in JUNE! This is a huge reason to wait. The OLED display doesn't need a backlight, so it uses less power, it's supposedly incredible from angles, and has better clarity and color.
MBP = reasons for waiting
Reason two for waiting, the battery technology used in the 17" MBP will probably make its way to the 15" MBP with its next update. A six-hour battery is worth the wait.
Reason three for waiting, official support for 8 GB of RAM. This is almost a guarantee. The consumer iMac now supports 8 GB of RAM, so the 15" MBP has to get that next. It costs a lot now, but a year or two down the road, it will be cheap and give you an extra year or two of life of the MBP.
Reason four for waiting, BluRAY, probably will not happen, but there is a rumor that 10.5.7 supports it, so anything is possible.
MBA reasons for waiting
Along with the OLED display, normal evolution would dictate 4 GB of RAM.
2.13 GHz Intel Core 2 Duo SL9600 (already released)
256 GB SSD drive.
Glass trackpad.
3G card built in!
Possibility of black anodized aluminum casing.
Possibility of two different sizes (13" and 15" rumored for six months)
There are a lot of great reasons to wait, but if you need it now buy based on what you most want.
If you want rev B MBA, try Best Buy or better yet Amazon. Some have said getting MBAs without lines at both sources. Amazon isn't much more than refurbished as they don't charge sales tax.
Good luck!