I prefer 20 best coins:-
1.LTC
2.XRP
3.DCT
4.XMR
5.MNX
6.KCS
7.PKT
8.SC
9.WAVES
10.NEM
11.OMG
12.PPT
13.DGB
14.DENT
15.AION
16.NXT
17.ARK
18.STRAT
19.BCC
20.XRB
Hopefully my suggested coin is good potential and you can select top 30 coins in coinmarketcap.