Well, apart from using VBox I'm also a very regular user of QEMU (again on XP, but also from Linux systems). If I just want to look up something in the base of a running TC system nothing beats qemu -cdrom tinycore_3.1.iso for ease and speed. OK, to be honest I've got batch files depending on whether I want to use KQEMU (which I do most of the time) or not. Due to the fact that I operate mostly older systems with CPUs which would not support KVM (which is anyway not on option on XP) I tend to use the old QEMU version 0.11.1 quite a bit, as it was the last one supporting KQEMU. OTOH, for some comparisons I've got the newer version 0.12.5 equally available. One point to remember is that the newer version of 'qemu-img' have fewer bugs, in particular if it comes to playing with non-native disk formats (e.g. vdi, vhd, vmdk, ...)
Now to get at least a little bit back to your question I'm not sure what your plans are, but for me to reasonably quickly undertake some tests where I don't plan to keep the result, I clearly prefer QEMU. But when the execution speed is critical I tend to go with VBox. It takes less time using just the keyboard (even considering that I'm a very slow typist) than all the time changing between keyboard and mouse (and I believe I know quite a few keyboard codes for VBox).
So for example I could create a blank hard disk image (e.g. via qemu-img create disk_50M.img 50M) and since I've extracted the kernel and the initrd file from the ISO image I can use qemu -kernel bzImage -initrd tinycore.gz -hda disk_50M.img -append "text syslog" (remember that's all just an example). The advantage of this is that I can more quickly adjust the boot codes at the next re-boot, until I have the preferred solution. This is something that VBox can't do, even so I've seen people asking for it.
Since I've done these kind of things now quite a few times, I'm happy to do the partitioning and formatting of a (blank) hard disk using only sudo fdisk /dev/hda and sudo mkfs.ext4 /dev/hda1 So to get ready to download extensions I just need to do sudo rebuildfstab ; tce-setdrive (and pick the correct device). So within lets say 2-3 minutes or so I've got a "fresh" test setup into which I can download extensions (some of which I have on a private TCZ mirror).
For sure I can achieve basically the same with VBox which is probably still a little bit faster than a QEMU 0.11.1 + KQEMU combination, and noticably faster than QEMU 0.12.5 under XP due to the lack of KVM. It's just depends what I'm planning to do, when starting a VM.
Unfortunately I'm not sure what you mean with "flaky", apart from the mouse issue I've already commented on in the other thread. In my view both VM work quite well for testing things out when it comes to TC. If one does not need the other "goodies" like better support of USB devices that the PUEL version of VBox has to offer it's somewhat amazing what QEMU can do (which I can fit in a 2 MBytes zip-file) compared to the 75 MBytes "heavy-weight" in the other corner. That aspect was one of the reasons why I gave up on VMware products, the bloat of these applications is just beyond me.