If you plan on sticking with the RF-603 triggers the YN-560iii is the best purchase, since it comes with a built-in receiver for those triggers. However, it pairs better with a YN-560-TX transmitter unit, because the TX can also let you control the power level on the YN-560III remotely from the camera. But it won't be able to control the power on your 430EXII, although it will be able to fire it if it's on an RF-603.
If you're okay with spending a bit more on triggers, however, then a better pair for the 430EXII Would be one of the Yongnuo TTL EX models (other than the single-pin YN-560EX) and bumping up to the YN-622C triggers. This way, you'd have full TTL, HSS, wireless 2nd curtain, and remote power control of both the flashes from the camera. Most off-camera flash afficianados will tell you you don't need eTTL (too much Strobist brainwashing) and you may not for studio-type lighting setups, but you'll want remote power control and the communication that allows that either has to be built into a flash/trigger pairing, or done through the TTL (i.e., non-sync) pin signals.
Of the three EX models you might want to consider--at the time of this writing--the YN-565EX (and MkII), YN-568EX (and MkII), and YN-500EX are probably the three most popular. The 565 and 568 both have the same power output--roughly between a 430EX and a 580EX, but only the 568 has 360 degree swivel and HSS, and only the 565 has a battery pack port. The 500 has 1/2 stop less power (so, say, roughly equivalent to a 430EX), HSS, no battery pack port, and only 270-degree swivel. However, Yongnuo models proliferate like rabbits, so check with the Flash Havoc blog to see what the latest developments are before buying.