I think both look pretty good for flatbar bikes. Make sure they have clearance for fenders and mountings for a rack.

Also, there is no need to go for more narrow tyres during the summer - a supple wide one will be wonderful (eg. Randonneur Hyper or Schwalbe Almotion).

I don't think frame material makes the biggest difference but I really like the look of many steel frames with the small diameter tubes compared to alu.