Metric simply due to the practicality. It is a PITA to get decent BSW fasteners or threading tools today. So when I come across poor threads , out with the Helicoil for metric. So then I can have a small kit of metric tools on the bike when I feel the need. That is 10, 13, 17 and 19 mm spanners. No funny hexagons from BSF, BSW, BA or what not, so you´d have to hunt for obsolete spanners for each standard. I accept UNF and that is it. Amusing for me all these discussions here about obscure threads which obviously lead to several problems in the workshop or on the road. No, I am not a collector of obsolete fasteners, rather of classic bikes and metric fasteners do not spoil the spirit of the bike - unlike modern components which everybody can see as non-standard. And no, I don´t care about compromised "values" with non-standard bikes once I have to sell them. Nobody can tell what the situation will be in 20 or 30 years in this respect, so I don´t worry about that.
Vic