Question: I have a Canon 550D which I've been using for around a year now. I really love it and have learned a great deal with this and the 18 - 135mm kit lens. But now with experience I feel the need to get some better glass. I won't be buying a new body any time soon because I figure investing in some good glass is more important. 

As I have looked around, I see quite a few good used L lenses I can get in ebay for good bargain prices. But I know that the EF lenses don't have the same focal length in the cropped sensors. Is it a wise decision to buy these EF lenses or buy the cropped sensor alternatives?

I have the following lenses in mind that I am looking to buy down the line from the canon range over the next several months.

16-35mm f/2.8L, 24-70mm f/2.8L, 70-200 f/4L.

Are these apt choices for cropped sensors? I know most pros with FFs use these but I am a bit skeptic that they will serve the same purpose for me. If so what are the alternatives for this that have almost as good image quality?

Answer: 
I am going to keep it simple.

1. Many people do it. In fact, I have seen most people using APS-C camera with a mix of EF-S and EF lenses, and less people use **only** EF-S lenses.
2. Expensive lenses offers **excellent** image quality with the trade-off of being expensive, inflexible (usually a narrow zoom range, may cause more frequent lens changes) and heavy.

Do you want to spend more money, carry more weight, narrow your zoom range, **just to get better pixels**? This is entirely up to you, but **honestly** and generally, such lens is not a **must** by people not getting paid doing photography.
There are a few factors to consider here. Firstly the EF L range lenses are considerably better build quality than typical EF-S lenses and the optical quality tends to be much higher too. On a crop sensor the 70-200 f4 L is outstanding. You do however have to remember when choosing EF lenses to apply the crop factor to get the effective focal length. That said lenses tend to last a lifetime if you look after them so getting EF will not limit you to crop sensors in the future. I started off with a crop body but now use full frame as well so my early descision to only buy EF lenses has paid off.

The two major drawbacks of EF lenses are cost and weight. EF lenses have to project a larger image at the sensor so tend to contain bigger heavier elements. The 24-70 f2.8 L forinstance is quite heavy and has the tendency to feel unbalanced on lighter entry level bodies. They also tend to be quite a bit more expensive roughly 40-50% more than EF-S of the same focal range and maximum aperture.

If you look at lenses as an investment then cost is less of a factor and in my opinion the better image quality makes up for the extra weight. However this is a personal opinion and you may come to different conclusions after trying out some lenses. This is the most important thing to do, go to a shop and try some of these lenses for weight and quality then also factor this into your descision.