Against skirmishers, flyers, large targets tough targets, FAST CAVALRY (especially) and small low armored units, the razordon is superior.
Against blocks of infantry and knights (heavy cavalry), the salamander is superior.
Make your own decision, thet both have their strengths.
Note that the razordon has a very cool stand and shoot reaction special rule. This can be used to to great effect by deliberately putting the razordon into the path of an on coming charge. Often provides unexpected results, like opponent running the hell away instead of risking a poo-storm of spines. This versatility, together with the fact that fast cavalry are both annoying and (normally) worth a health amount of victory points (5 fast cav will normally equal or go over the cost of the razordon, and its quite possible to wipe a unit of 5 out in a turn), as well as the fact that fast cav can charge and kill a unit of skink skirmishers with relative ease, lead me to believe razordons are the more reliable to put into your "locked out" tournament lists.
Contrary to above post (apologies, no offence or flaming intended).
Using razordons on their own (units of one) is the best way to field them. Its only 75 points for a deployment. Only 75 points to die when it gets charged. Too annyoing to ignore but not worth many victory points. Still causes fear as well as a unit of 2 or 3. Takes up less space in deployment zone and in your battle line. Less points in rare units, leading to (normally) better scores in tournament composition judgments.
I have 2 units of one in my army. I personally love them ;p.