Having had a garden railway for a few years I would suggest Stainless Steel. I have brass (Aristo Craft which I like), but hard to keep clean. I wish I would have known about the stainless steel track years ago, because that is the way to go in my opinion. Very easy to keep clean. One of the suppliers is
You can do a google for more suppliers.
Also on another note make sure that you have a good power supply. Depending on the size of your layout you may need to run power leads about every 30 to 50 feet. I figured this out by trial and oops not enough power.
I assume that when you say "G scale" you require #1 gauge track.
Peco do two ranges of #1 gauge track
1) The #1 gauge "standard gauge" track is intended for #1 scale (1/32) and is Code 200 nickel silver. The older LGB equipment has deep flanges and may "hit" on the rail fixings. This track is similar to the Maeklin #1 track. Sleepers (ties) are about 9mm wide by 4mm thick and there are 13 per foot. I have found the track to be slightly undersize. Peco use a gauge of
1.75" which is 44.45mm, rather than the more common 45mm.
2) The "narrow gauge track" (45mm gauge) uses Code 250 nickel silver. Sleepers spaced at 8 per foot.
LGB Code 332 brass. The older rail had a high amount of lead content, and tends tarnish quickly. Fairly hard rail though. Ties are about 12mm wide by 9mm thick and there are 11 per foot.
USATrains Code 332 brass. Fairly "bright", possibly because of a lower lead content. Ties are about 12mm wide by 9mm thick and there are 10 per foot.
AristoCraft Code 332 brass or stainless steel. The brass rail appears to be the same as the USATrains, and is fairly soft. The stainless steel is harder. The Ties are about 9mm wide by 8mm thick, and there are either 11 per foot (Euro style - to match LGB) or 14 per foot (USA style). Much wider range of track lengths and curve diameters than USATrains.
There are also various other brands on the market, but these are the one I have used.
Currently, I am using AristCraft stainless steel track. I handbuild my first batch of turnouts using AristCraft brass rail (except for the switch blades, which I use LGB rail as it is harder and doesn't bend as easily), but am going to try stainless steel for the next batch (just need to come up with a good solder material and technique).
LGB, AristCraft and USATrains will all join together, although there are slight differences in the rail base width and the web thickness. I would suggest keeping each brand in their own sections, to minimise the inter-brand connections. Both AristCraft and USATrains use a screw to lock the rail joiner to the rail.
MicroEngineering offer Code 250 and 332 aluminium, and Code 250 nickel silver.
I would suggest getting a copy of April Garden Railways and check all the ads.
My choice is AristoCraft SS. Both for cost and cleanliness.