It depends on
why your DIR655 is "unreliable."
If you have to reboot it a lot, it may be overheating due to age, in which case any new router will be fine. Same if your cat peed on it or something.
On the other hand, if it's locking up when under heavy load from a number of users (BitTorrent, say) then a new router that is similar in terms of RAM/CPU would probably suffer the same kinds of problems.
If you're just having WiFi range issues, a new router with big honking antennae and radio will help your client devices "see" the router's wifi signal better, but
it won't help those same devices punch a signal back to the router. So, depending on what the limiting factor is, you might not see any improvement at all in wifi reception.
The
Smallnetbuilder review of the DIR-655 makes it sound like it was a pretty awesome router back in the day. That said, technology marches on and a new midrange to high end home router will probably be a more capable piece of hardware.
The danger as a shopper is that there are going to be any number of low-end routers you can get that won't even be as good as your old one.
Personally, I think an Asus RT-N66U would be a good move.