How to pick correct operational amplifier as unity gain buffer between TLC1543CN and LDR
Speed

An LDR is generally a slow device (many ms response time). 2Mhz bandwidth (=4Mhz sample frequency) is useless and unattainable. The ADC does not support it: its conversion time is 21us, which -if you could fully use it- impies a bandwidth of around 20kHz. But even that is extreme overkill for an LDR. Speedwise any opamp will do.

Supply voltage

When you have a positive power-supply only, you will have to choose a so called rail-to-rail opamp. Normal opamps often have trouble working on a single 5V supply.

Dynamic range

Using a unity gain buffer is fine, but you lose resolution because the ADC input range is not fully used...

Imagine a divider of the LDR and a 5k resistor to ground. In the dark case the output of the divider will be: Uin*5k/(500k+5k) = close to 0V (good). But when the LDR is lit, it's resistance will be 5k, and the divider-output is only half of the supply-voltage. So you use only half of the ADC-steps.

To alleviate that you could use more gain. You can use a non-inverting amplifier configuration with a gain of two instead. This will "scale up" the output to the full ADC range at the cost of two resistors. It doesn't influence the choice of opamp.