garmin sl30 and garmin gnc 255

[beecucaracha]

I have sl 40. Wanting to install sl30 or 255 for back up nav source and ifr approaches. Any suggestions regarding sl 30 as opposed to 255? Will vor navigation remain for years, or should I consider garmin 300xl or 430w? 300xl is gps, but will skyview control radio frequencies? 430w is expensive for my limited use.  Comments? Newbie. Thanks in advance for any replies.