Compared to the Atrox, the older science vessels like D'Kyr and Nebula aren't going to have a lot of selling points and definitely can't compete in the size or number of toys department. The Odyssey Scientific is pretty good but is not a 'proper' science vessel. It behaves more like a cruiser with an advanced sensor package and is IMO, way too common and most Odyssey builds I've seen flown by non-Fleet personnel are a bit weak, to tell the truth. You got to make sense of how to use the universal LTC bridge officer slot to spec the ship right.
If you don't think too highly about the Nebula's selling points, you really havent given it a fair shake yet. What it gives up in novelty, it gets back in spades in flexability/adaptability and toughness. There are quite a few people who use these things to great effect as a Sci-PvP ship, as well as STF sci-ship.