To stick or to switch topics I'm currently starting my PhD and I'm contemplating whether I should stay with my current advisor and topic or switch before its too late.

Current subfield


The recent work in this subfield has been very cool and my advisor's strong track record in this area was what attracted me to his lab.
I don't have much of a background in this field. I feel like I'm struggling when I do research in this field, and I'm not sure how effective I would be if I went into this long term. (I don't think I'm playing to my strengths if I entered this subfield).
I have heard from others that academic job prospects in this subfield are lower than other areas.


Other subfields


I feel more comfortable with other subfields and I think I would be playing more toward my strengths even in certain other subfields where I have less of a background.
The labs in other subfields are more popular amongst grad students, and I suspect each student gets less attention than they would with my current advisor.


Any advice on whether to stay and switch? Is it best to wait and switch, or switch ASAP.
Let me react to some specific comments

I don't have much of a background in this field. I feel like I'm struggling when I do research in this field, and I'm not sure how effective I would be if I went into this long term. (I don't think I'm playing to my strengths if I entered this subfield).

If you're just starting your Phd, I'd be surprised if you were an expert in the field, no offense. There is much to learn, and most early grad students - good and bad - feel they're struggling. The important question is are you struggling because it's complicated (good!) or because you don't care about the topic (bad!). If the latter, consider switching. 

I feel more comfortable with other subfields and I think I would be playing more toward my strengths even in certain other subfields where I have less of a background.

One's comfort zone is seldom where significant progress is made. Again, if it's an interest issue, consider changing, but if you just feel overwhelmed by a new research area, consider embracing it - you will learn a lot. Moreover, perhaps you can bring your 'other sub fields' strengths to bear on your current subfield. Some of the best students I've known have used analyses and thought processes foreign to their immediate field. 

The labs in other subfields are more popular amongst grad students, and I suspect each student gets less attention than they would with my current advisor.
Any advice on whether to stay and switch? Is it best to wait and switch, or switch ASAP.

If you're set on switching, do it asap. Just make sure your motivation is sound. You want to be able to stand out, for sure, but every field is going to have difficulties. It's a Phd.  If it were easy, everyone would have one.