I used the free online scan, no need to purchase or subscribe to anything. I used to use AVG free for my desktop A/v solution for years, but have switched to Avast free, following some comment around the web about AVG not being as successful as it used to be. I can't comment on that, but Avast seems to catch things just fine and is pretty comprehensive. I am not so keen on the Comodo free solution as it seems to slow the machine down a bit, but it's an old machine anyway. I don't know of any reason to actually pay for any of these solutions, in any case, unless you're in a corporate environment and can really justify doing so. Firewalls and constant monitoring are often free now and included as part of the packages, making them ideal for home use. I'd suggest looking at free options before you subscribe again, frankly, and maybe try some out. I've run Avast alongside another system and not had any conflicts, that may be worth a look.
By the way, the main problem I had was that I'd forgotten I'd reinstalled Windows a while back, and when I'd done that, I'd also forgotten to disable System Restore - a feature I've always regarded as one of the most dangerous "benefits" of XP. Usually I disable it right away, but this time I'd forgotten. So of course XP was kindly restoring all the bugs I'd just taken out, every time I restarted.
Absolutely the MOST useful thing that the "removal tool" could and should have done, would have been simply to remind me to disable System Restore and then reboot. When SR is manually disabled, all the existing restore point files are automatically deleted, taking with them all the viruses and Trojans that are lurking there just waiting to come back again. The trouble is, MS touts System Restore as a big advantage, so they can't really advise you to turn it off without looking foolish. Not that they're entirely unused to looking foolish, just not intentionally.