I'd like to share something about TradiConsult (maybe especially applicable to PhD living & working in Kanton Aargau):

I'm a PhD living in Kanton Aargau (AG) and insured with TradiConsult (TC) since January 2005. The health department of Kanton AG (HDAG) gave me a 3-year exemption from the general Swiss health insurance (Befreiung von der KV-pflicht in der Schweiz). After this I have to go to a Swiss general health insurance company. So far I have not much to complain about TC. They paid my medical bills alright.

My colleague from France who started her PhD in September 2006 (she also lives in Kanton AG) went for Swisscare initially, but then came the round letter earlier this year stating that Swisscare is not accepted in Kanton AG anymore. So she tried to change to TC, but did not get an exemption from the HDAG either. The HDAG said they "recently" put TC on their black list (something about money problem between TC and kanton AG, I don't have the details, though).

I'd recommend any PhD who is considering to get a cheap Swiss health insurance to confirm first with the health department of his/her respective kanton before signing the contract. It may be a hassle to get the money back from the insurance company in case an exemption is not granted.