Depends if you need/value speed or shallower DOF, or you prefer more reach, and a more compact/lighter package. I have both and use both quite a bit depending on what I'm shooting, where I'm going etc, such as if I'm landscape shooting, or going to an indoor sporting event, or perhaps an outdoor event in good light or shooting a portrait etc
70-300 does things the 70-200 can't and the 70-300 does things the 70-200 can't (in regards to lighting the load of your bag)
After the G1, I'm never going to take the 14-24, 24-70 or 70-300/70-200 with on for travel again. Too darn heavy and just not worth it. 7-14, 14-45 and 45-200 give me all the same range and the whole kit weights less than the 70-200 alone.
Millsart, I do all my photography traveling, I have followed the m4/3 cameras quite strongly, but have yet to see them regularly render the detail of excellent FF DSLRs, would love to see posts of your m4/3 shots.
I didn't save any of the files, but when I got the G1, I tested it pretty in depth against the D3/D700 and my D5000 as well and really couldn't tell the files apart, at least under ISO400, and from a little difference in DOF.
The Lumix glass is as good or better than most Nikon consumer glass. The 45-200 for example is next to impossible to tell apart from the 70-300 VR.
The m4/3 sensor actually renders a bit more detail then the Nikon DX sensor, at least if you shoot RAW. Its not quite as good as the FX sensor but its really splitting hairs when it comes to resolution and there is no way I could pick which was which if just shown a few shots blind.
The FX sensors still are leagues better at higher ISO, than both the DX and m4/3 bodies, but it really depends how often your shooting at high iso.
In my daily news and sports work, especially this time of year, sure I'm at 1600 or higher constantly, but for my landscape work I'm always at iso100 and off a tripod so its a null point, at least for my needs. Actually I'm often using a ND grad to get even slower shutter speeds than what ISO100 can offer for moving water.
m4/3 is about on par with the rest of the 12meg sensors on the market. Better in some ways, worse in others, but as a whole its pretty solid. Its certainly better than any 8 meg DSLR's we had a few years ago.
The size/weight are just brilliant though. Being able to have a stabalized 90-400 equiv lens of pretty good optical quality, on par with a 80-400 really, that cost only $300 and weights under 1lb, plus that you could carry in a jacket pocket is so nice. Same goes for the 7-14mm giving you a true 14mm equiv FOV but weighting only bout 9 ounces and again being pocket sized.
I've yet to try the 20mm f1.7 but have heard its really nice as well, 40mm equiv and only 1" thick.
I also want to get an adapter to try my 85mm f1.4 AF-D which would give the equiv framing of 170mm f1.4. Obviously the DOF isn't going to be the same because of the subject to camera distance to get the same framing, but, I'm thinking it might at least be similar to my 200 f2, and that lens is over 7lbs.
If you want a light travel kit, look at the 16-85 with 70-300VR. Neither are fast but on a D300, you can bump the ISO up with little concern. If your body is FX, then a different wide option would be needed.
If I were putting together a system just for travel, it would be D5000, Tamron 17-50mm VC f2.8, Nikon 70-300mm VR, SB-600, polarizer, 500D. Compact, flexible, capable. For a lens, why aren't you considering the Nikon 80-200mm f2.8 AFD? Or, 80-200mm AFS? It's much more compact than the 70-200mm VR. I own the 70-200mm VR and don't consider it to be a "travel" lens.
I usually shot with D700 and very good quality glass but when traveling I've got tired to take tons of equipment with me, so I have a "ready to go" National Geographic bag with a D5000 camera equipped with Tamron 18-270 VC. Additionally I take a Nikon 35mm f1.8 for low light situations and a Tamron TC 1.4X. This TC pairs unbelievable well with 18-270 on good light conditions and even Tamron plays in a different league than Nikkors I am very happy with this versatile and very light travel kit. When I know that I'll do lot of landscapes I add Nikon 10-24mm and that's all.
For full frame Tamron has a 28-300 mm VC that's also very good. Hard to believe but VC from Tamron beats VRII from Nikon. You should give a try...
This travel kit is also good in terms of safety... I'll make a stroke if one day someone will still my bag with D700, 70-200, 85/1.4 and 50/1.2 AIs. :-) But for sure I'll survive if unfortunatelly I'll loose the other bag.
