Only thing I can think of is latency. I believe the pool's server is in the usa so probably westhash would be better but I'm no expert.
Nicehash recommends westhash for people in the US while nicehash is the rest of the worls.
some pings from north europe(LTE connection used, ping to my local operator 15ms):
(west/nicehash seems to have some fast fibers..)
Pinging westhash.com [108.162.200.77] with 32 bytes of data:
Minimum = 24ms, Maximum = 56ms, Average = 38ms
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Pinging nicehash.com [108.162.201.7] with 32 bytes of data:
Minimum = 23ms, Maximum = 45ms, Average = 34ms
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Pinging solo.ckpool.org [104.200.24.180] with 32 bytes of data:
Minimum = 207ms, Maximum = 234ms, Average = 223ms
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Pinging eu-01.miningrigrentals.com [188.226.209.186] with 32 bytes of data:
Minimum = 57ms, Maximum = 66ms, Average = 61ms
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Pinging us-central01.miningrigrentals.com [50.7.11.74] with 32 bytes of data:
Minimum = 148ms, Maximum = 169ms, Average = 160ms
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Pinging us-west01.miningrigrentals.com [107.170.196.237] with 32 bytes of data:
Minimum = 195ms, Maximum = 225ms, Average = 215ms
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Pinging us-east01.miningrigrentals.com [107.170.50.27] with 32 bytes of data:
Minimum = 121ms, Maximum = 152ms, Average = 140ms