In my opinion the best strategy is a mix of auction and negotiation. Auctions to buy 4* low 5* ft and negotiation to buy ready players with white skill over 170%. I usually fill my starting 11 with 6 young fast trainer (18-21 yo) that I train until 130/140% and the rest are older player with high white skills. This way I won't run out of green packs to train the young players and I won't run out of tokens to buy players on negotiation. In rare cases I bought the 79T weekly recommended player (it must be exactly what I need in that moment). Every season I replace 3-4 players.