Canon EF 100mm f/2.8L Macro IS USM

The 100mm macro lens from Canon is still the reference on the market and it's hard to offer a better lens than this.

The lens offers the optimal sharpness at f/5.6 up to f/8 with >2300 lines which is really great. It has an internal focus system which means that no tube comes out of body during focusing.

Apart from that the lens has an internal stabilizer and an ultrasonic motor for fast and precise focusing. The minimum focus distance is 30cm which is far enough for the most insects. Users which have an APC-S sensor can be happy about the crop factor which means an equivalent of 160mm focal length.

The dust and splash water protection is an additional advantage of the lens.

It's not the cheapest one but it's still the reference on the market.

You can shoot amazing images with this lens, highly recommend.