Ortmanns are an excellent choice but you need to have some metrics to get the excellent performance out of them. I.e. no WD40, the track must be cleaned regularly from dust and you must rubber the track with something like 1000 laps before having the decent grip.
Slot.it Silicone tyres are also very good and do not require excellent cleaning of the track. They also favour WD40 on it, no problem. But you cannot have cars with Ortmann and silicone tyres since the latest take away the rubbering in the track.
A very good alternative is NSR tyres, very soft and excellent grip. They are on other end wearing faster than other kind of tyres.
I have today only Ortmann and NSR.
Off course it really depends on the type of track you have.
I get my tyres in Sweden afrom SlotCar4fun.se and in UK from Pendleslotracing.co.uk or rsslotracing.com.
All of them are good reliable and have good prices.
I almost forgot to mention that Otmann tyres are also cheaper.