NG
+ easier to build
- see MG's "+"s

MG
+ color separation is better than NG (Most of the parts are molded in the correct colors) This won't matter if you are painting it.
+ proportions are normally better compared to NG
+ more details (panel lines, stickers)
- more expensive
- takes longer time to build.

Though if this is your first time building a Gundam, I guess you should start with a NG. A NG can look as good as a MG with enough effort put into it.

There is the Metal Build of the Gold Frame Amatsu... though its not exactly cheap...

Like jloi said, the NG is just the 1/100 version of the 1/144 HG. If you've built a RG before and like the details, you might be disappointed with the lack of details on it on the NG. There is also the fact that the NG doesn't have a flight pack (note that the MG flight pack is different from the HG Red Frame's Flight pack) Personally I would go with the MG version, though that's just my preference.

To each their own.

Did you happen to see the rg strike freedom expo? And
If you did, how much was it?

Went there this morning. They had a label at the counter there saying only the only Expo items available left are RG Exia and the HG Gyan.

I PO-ed Altron from G-Wing and received it last week from them. Their site might be down, but I think they will still notify you via e-mail when it has arrived.