Get the international version if possible.GTi9300. Not something like GTi9300G, GTi9300X and so on. Make sure to check the model number. Because all is labeled as Samsung Galaxy S3, only model number can tell difference. 

If I"m not mistaken, that was fixed by Samsung through a software update making the G version have no advantage over the normal version.
Best bet is always to go with the normal international HSPA+ version which is I9300. Don't take any other with letters following the model number if you can. Check the back of the box before buying. Taking niche versions would mean less or no after market community support.

get the one withOUT the G

They cost the same in terms of the retail price suggested by Samsung, what shops charge is of course depending on the owner.
Last year with the S2, the I9100 was launched first here in Malaysia, that's the international HSPA+ version of the S2, then Samsung Malaysia quietly stopped shipping that stock to stores and sent the I9100G instead which had a different dual core processor clocked at the same speed claiming it won't affect anything but that is of course not true.

I foresee something of the same nature might happen again this year with the S3. So unless your willing to take the risk, you'd better buy the phone as soon as you can if you want it to void such a situation. Your only choice if that happens is to import it yourself or look for shops selling grey import or buy second hand if you want the normal version. Of course pay attention to the box and model number when you buy them.

Should be no price difference but it is up to seller. You should get the phone as soon as it is start selling but try not too hurry. Make sure you check everything before buy. Model number, warranty card and period , receipt, SME or AP set, free gift etc.
If S3 follow S2 trend, first S2 non g model selling is international version, around 2k+, then three months later, g version come in with price RM1899.

maybe, since now non G version expensive than G version (correct me if I'am wrong)
furthermore, yes get the phone ASAP so that it won't repeat the same case as s2

and don't worry so much, just wait it release and see what the model number