There are loads of good phones on 3, but you get what you pay for.
If you go on 'pay as you go', you'll get one of the older phones on the cheap, and have the same issues you'll have with any poor phone. Also, i'm not sure if you get many cross network minutes this way.
If you're willing to take a contract, you can get very, very good phones like the LG flip range, or the new Motorola range, such as a Moto a1000 PDA for free (or very little) onn a very cheap contract.
The mythology that the calls drop all the time, and you can't get coverage normally comes from people who only had 3 at their infancy, or live in the sticks. The only major problem with 3 is the call centres, as they are in India.
As with anything, like I said, you get what you pay for phone-wise, and if you are willing to put up with the call centres, then 3 is a very good deal.