Hi,
Depends how its been made, some are just not up to a bit of bumping (poor build quality) and some can't drive an external speaker loud enough.
Others are very simple internally (the very cheapest ones, and some well known branded ones) using SDR - a very wide front end with poor filtering - which picks up any and all electrical noise so you can't hear much. This reduces your range.
Choose something which is robust, been reviewed by others, small enough to fit where you want without getting in the way, and has at least 12watts output to the external speaker jack.
nice to have is a 'lock' which locks the front panel in case of knees / whatever bumping it, and channel scanning / dual watch. Everything else is going to be a gimmick and you probably won't use them.
Don't buy the quick-release antenna things that maplin sells, because they rust and cause problems for the radio.
Kind regards
Clive