I mostly play by myself, so matching other instruments isn’t really an issue here. My favorite whistles are my low d’s. I just wanted to know what everyone here thinks is a better sounding key: Bb or Low G?
I’m looking at the Dixon polymer ones. I’ve had great experiences with his whistles, but I can’t decide which key I will like better. Unless I just get them both… 
I like low G much more than Bb. Unfortunately, I don’t have any low G yet. If I were you I’d definitely go with it.
I’ve owned Dixon tunable polymer whistles in high D,C,Bb,A,G, low D and low C. With the exception of the low C, they were all very useful whistles. Nice sound at a decent price. I liked the low G quite a bit, my favorite of the lot, but then the low G is one of my favorite whistles regardless of maker. Just one person’s opinion.
Feadoggie
You will want both. I have both and my Dixon polymer Alto G is one of my favorites of my 30 plus whistles.
Don’t be chicken . . . grab’em both 
I like my Hoover Blacktop fipple on my brass Generation Bb. I mostly play it solo. My low G is lovely too.
Add low F to your list. My low F holes are just about the same spacing as my D chanter, so you will be ready when you order your practice set.
You do know that the tinwhistle is a gateway drug to the uilleann bagpipes, didn’t you? 
I’m going to go for the G. Thats what I was leaning towards anyway.
How big is the hole spaceing on Low G’s? Do you need to use pipers grip?
Not a problem at all for me, just curious