I am starting this sweater for my niece and in the pattern it says:
Row 6: P across, increasing 5 (6, 6) sts evenly across the row; 41 (45, 51) sts.
but it doesn’t specify which increase I should use. Does that mean that I should choose for myself? If so, any suggestions? I’ve worked several increases before, but I’m not sure which would be best.
I’m kind of new to this, if you can’t tell 
When you get this sort of instruction, it means that it doesn’t matter if you’re off a stitch or so, just as long as you make the required number of increased stitches.
How I do it: If it’s only a few stitches like 5-6, I divide the row to make the increases on in half. Then I divide the number of stitches in half (if odd, then the odd stitch increase will be directly on the division place of the row) and space them approximately (say, 1/3, then 1/3, then 1/3 again) before the half-way mark. And repeat the thirds on the second half of the increase row.
Not a precision-type of operation. Approximates work just fine.
Dot
ok, thanks 
I couldn’t believe that I was six rows in and already hitting a road block haha
And it doesn’t matter which increase you use, just as long as they’re more or less evenly spaced.