Craig, I'm sure you're already aware of this, but ricotta doesn't really melt, at least, not in the traditional cheese melting sense. We're talking about completely static cheese particles suspended in liquid. It's the size/consistency of the these particles and the quantity of liquid that dictates flow when heated. This is why blending/processing with liquid is so popular. Smaller, wetter particles will flow better during baking.
The absolute worst case scenario is dry clumpy ricotta- which you experienced first hand. This can be brought back to life, though, with sufficient blending and liquid- to a point.
Particule texture varies widely- you can have soft, velvety particles vs. hard grainy ones. Particle consistency relies less on source (whey vs. milk), then it does on cheesemaking skills and freshness. Whenever you make this kind of cheese, you're looking at very tight tolerances when it comes to curdling agents and heat. Too much curdling agent (usually acid) and you denature the proteins excessively and you end up with a rubbery particle. Too much heat, same thing. It takes tremendous skills to end up with something soft and velvety- skills that, imo, take months of cheesemaking to acquire as well as an understanding of the chemistry involved. It's way more than your typical ricotta recipe of just heating the milk, adding the acid and collecting the curds. Way more.
The other aspect is freshness. Purchased ricotta, over time, will get grainier. I can't speak for the rest of the country, but typical supermarket brand ricotta, if used close to the day you buy it, is usually pretty darn tender and creamy. In my area, it's always better than Polly-O and Sorrento. That's what I'd try first- with some blending and some liquid- cream, milk, olive oil, etc. If that doesn't work well for you, go with the national brands.
Imo, instead of seeking out a special brand that might be a bit more expensive and not have great turnover, it's preferable to get the freshest cheap stuff you can find.
