The most sought-after WTs of course remain by far those in combination with a rare handcraft, i.e., the 5131 and 5231 iterations (as it's also clear from the secondary market, even for the 5231). My best advice is probably to go for a 5230 if someone wants to enter the "Patek WT world" right now, which are still *very* widely available at virtually any AD...;-)