12AU7A, 12AY7A, 12AX7A, and 12DW7A are all twin triodes, with identical pin connections. The only major difference is the available gain. The ECC tubes are the European equivalents. There are some audible differences among different brands, and years, of tubes with the same part number, so you could spend a lot of time (and money) experimenting with used, New Old Stock (NOS), and new tubes. If you like what you hear from what you have now, that's good.

If you have some tubes laying around, and you're curious, swap 'em in and try 'em out. Low-gain tubes will clean up the tone, and give you more headroom before they distort, maybe with lower output. High-gain tubes will distort more readily, and will drive your power amp harder.