difference between manhattan and euclidean distance on single linkage cluster ?

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C#

what is the difference between manhattan and euclidean distances calculations on single linkage cluster ?? which one is preferable ? i wrote a program for single linkage clustering and used both distances calculations ,, i just see that when i want to divide clusters like 5 clusters or 6 clusters by stopping iterations ,, i seen clusters has different members at the same iterations.
like this :
for euclid
.....İTERATİON ..... :39

Cluster 0

1 7 19 33 46 47 20 27

Cluster 1

2 8 28 34 44 17 31 5 25

Cluster 2

3 11 12 37 39 29 42 15

Cluster 3

4 6 14 32 41 30

Cluster 8

9 16 35 43

Cluster 9

10 21 36

Cluster 12

13 26 40 18 22 45 24 38

Cluster 22

23

and for manhattan :
.....İTERATİON ..... :39

Cluster 0

1 7 20 33 47 46 19 27

Cluster 1

2 8 28 34 44 17 31 5 25

Cluster 2

3 11 12 37 39 29 42 15

Cluster 3

4 6 14 32 41 30

Cluster 8

9 16 35 43

Cluster 9

10 21 36

Cluster 12

13 26 40 18 22 45 24 38

Cluster 22

23