I'd be tempted by those Steve Sinner rests. I have several straight rests that are in constant use, including a couple from Robust. The top hardened rod is great for finish cuts, and is my preference.
I also use several outside curved tool rests, including one from Robust and a couple from Oneway. The curved outside rest from Oneway is a bit too large for some work. I ended cutting down my first one, and then ordered a second one. From my point of view, a good curved rest is essential for perfect cuts, simply because it will be closer to the curvature of most bowls. Straight tool rests are not as good for following a curve, because it's better to maintain an equal distance (or as close as possible) between tool rest and the workpiece through the length of the cut.
For me, inside curved tool rests are not as important as outside curved tool rests. I've got the Robust, Oneway, and the J-hook rest Al mentioned. The J-hook is great when it's needed, but not very often. Sometimes I use mine as a straight tool rest when the conditions make it a good choice to do that.
Overall, I'd suggest anyone contemplating tool rests to get a curved one along with some straight ones, and do some experimenting with it. The outside tool rest is important for me to have, and to a lesser degree, the inside tool rest. Like all things woodturning, everything, and every technique, and every style, is subject to how an individual evolves in their work.
I use a 4" straight Robust tool rest more than any other straight one, so that's where I'd start if I were buying.....but, longer straight tool rests are very important to have, too.
ooc