My experience with st léger is that seepage may be a bigger problem than the weather during your stay. This may be even more critical during late april as the best warm weather sectors (face nord, la baleine) are also the ones featuring the most tufas. Face Est may also be really good in the afternoon, and less prone to seepage (though two of the best routes, "dis moi..." and le Nabab, suffer from long-drying water streaks)
Tarn is a great alternative and weather wise it is just the opposite...less climbable if it's raining, but dries faster.
Accommodation tips for at leg:
-if you have a van stay in the designated van area, just after the village on the right inside (driving from the crag)
Otherwise, the gite on the crag's parking lot is hard to beat
http://bergerie-des-salamandres.com/
