I don't have enough restraint to be one of those people who only uses one foundation at a time. Depending on my needs that particular day (Do I need a base that photographs well? Lasts a long time?) and how I'm feeling, my choice of base changes accordingly. Here a are few of my favorite bases and the occasions on which I most prefer to use them. (Note: not all shades match me at my current NC20 state.)
The natural day-to-day foundation.
The Revlon Nearly Naked Foundation (shade 130 Shell) is a great light coverage foundation that feels weightless on the skin. It has a natural finish that is neither truly matte nor dewy - it's just somewhere perfectly in between. It's perfect for everyday wear when you just want a bit of coverage that will never look like you have foundation on. I always wear this over primer and with powder on top to make it last a decent while on me, although I will say that the lasting power is nowhere near as tragic as people make it out to be, at least not on me. This has SPF 20.
The higher coverage daytime base.
When I'm needing a little more coverage during the daytime, I turn to either the Dior Diorskin Nude BB Creme (shade 002 Fair) or the Chantecaille Just Skin Tinted Moisturizer (shade Bliss). Both are light to light/medium coverage and have dewy, luminous finishes. The Dior has SPF 10 and the Chantecaille has SPF 15.
The non-liquid daytime foundation.
If I'm in a rush or feeling particularly lazy and can't be bothered to slather on a liquid foundation, I'll use the Laura Mercier Mineral Powder Foundation (shade Real Sand). It has light coverage and despite being a powder, it doesn't look powdery or cakey on the skin at all. It has a natural matte finish that still lets skin look like skin. The only downside to this product for me is that I get quite shiny after about an hour and a half and need to blot more often throughout the day than I do with other foundations. This has SPF 15.
The lightweight nighttime foundation.
My pick for this category also happens to be my HG foundation, Make Up For Ever Face & Body Foundation (shade 20). It has light coverage that is easily buildable without looking cakey, and the finish could not be any more like skin. It is incredibly natural looking and lasts the longest on me out of all of my foundations. It does not contain SPF, which makes it suitable for night outings with the potential for flash photography.
The higher coverage nighttime foundation.
When I want more coverage at night, I look to the Bourjois Healthy Mix Serum Foundation (shade 53). I love this foundation. It has medium coverage with an incredibly natural yet glowy finish that doesn't make me particularly oily. This also does not contain any SPF, so it doesn't flashback with flash photography.
As you can see, in general, I like to have a little bit of SPF in my daytime foundation and none in my nighttime options. I also prefer lighter coverage foundations, and medium coverage is typically the heaviest I'll go. I have combination skin with an oily t-zone, so I typically wear my base makeup over a primer like the Laura Mercier Oil-Free Foundation Primer or the Smashbox Oil-Free Photo Finish Foundation Primer and powder lightly on top through my t-zone, if not all over.
All of the products that I've reviewed more in-depth before are linked above :)