We go to Spain every winter/Spring but have never stayed in the Alicante area. Friens have said the sites at beni cassim and Denia are good - you can see details in CC Europe Spain and other handbooks. It depends on what you want from a site - full facilities, pools, bars etc. or very simple basics sites - not too many of the latter.
The early Spring weather can be better a little further south say around Murcia, Mazzaron area, or even further where we go around Mojacar. The costal strip leading down to the extreme south east corner Cabo de Gata also has a number of sites.
It will also depend on whether you rely on site facilities for showers etc. or use your own in-van as we do. This means you can tolerate less than perfect public facilities at the expense of water collection and disposal and possibly having to wait. We are in a minority with this approach but freedom of choice is one of the great things about this lifestyle.
If going for the first time I might suggest you don't book in for your entire stay in one site. Take some time to get accustomed and after that consider going further south to see a few other sites. It is quite likely that you will find one that somehow 'clicks' with you andyou will return for several more years. Travelling is easy and you could easily go Alicante to Murcia inside a day in comfort.