I've used Marathons & Racers on my 20" Dahons, the Portland (700C) has Supremes on at the mo. I've had no bother with the Racers (admittedly only done about 300 on them this year, plus a few hundred with them on my old Jetstream before that), unlike Auntie Helen. Results clearly vary!
Marathons are brilliant value for money, considerably harder wearing than Racers or Supremes and not much slower. Supremes are excellent too though- pricey for sure, certainly in the UK (I got mine from bikediscount.de and saved about £10!!), but considerably lighter in larger sizes (a pound less weight in 700x28 than Marathons). Higher wear, but also higher speed. Either would be a great choice.
