It depends, like it always does. If you need Ray-Traycing go for the RTX 2080TI or you aren't care about it, the 2080TI SLI should be a killer-Rig.
BUT if you want to upgrade down the line to, like 2 Way NVLink RTX 2080TI, you should go for the RTX card. Pascal was out about 2 Years now so the Architecture of Turing improved significantly. I would wait the month and go with a 2080TI but if you want a Rig in its full SLI glory the two 1080TI's should serve you well.