Garmin 530
I,m not a great fan of the Garmin 430 the main reason being that it trys to pack to much imformation into to small a space.
The 540 has the display space with room for much more that is likely to come along in the near future and would seem a better investment to me.
Having used the Garmin along with a King KX165a NAV/COM I found the audio quality of the King a bit better and feel that the TX range will be better ( but I cant prove that ).
What ever you buy pay the extra and get an avionic cooling fan fitted , a few quid spent now will save you thousands in the future !.