I am debating on what one to use.
They say you need a certain feat to do a full attack with a crossbow (don't remember what one) would you need that for a repeating crossbow?
Also you can only shoot a heavy crossbow once every other round unless you take rapid reload but you can reset a Repeating crossbow as a free action.
Also can you take rapid reload to reload the magazine to the repeating crossbow? or use the spell abundant ammunition on the magazine?
So is it better to take a regular crossbow and take that feat or use the feat to use a repeating crossbow?
i am not the primary ranged fighter (that's a gunslinger). i am in fact the bard and i have low str that is why i am going with a crossbow, it can do more damage than i could with a bow.
Crossbow Mastery is likely the Feat you mean. If I remember right it lets you reload the Crossbow as a free action.
Light crossbow + rapid reload gives you as many shots per round as you can make attacks in a full attack action.
Repeating crossbow + proficiency gives you the same up to a limit of 5 shots where you need to reload the magazine. Already its much worse than the regular crossbow. Sure you could add crossbow mastery or abundant ammunition, but you only pay extra taxes to get where you could have been with a regular crossbow long ago.
Heavy repeating crossbows at least get you 1d10 damage but once you crunched the numbers I'm pretty sure a light crossbow with rapid reload will get you the better value.
Like Threeshades said, you have have two real options here.
1) Go with a Light Crossbow and the Rapid Reload (Light Crossbow) feat. It has range 80', 1d8 damage, 19-20/x2 crit, and the RR feat makes reloading a free action which, according to the RAW, allows you to fire your full compliment of attacks on a full attack action.
2) Go with the Heavy Repeating Crossbow and Rapid Reload (Heavy Repeating Crossbow), Point Blank Shot, Rapid Shot, and Crossbow Mastery. This is a much heftier investment, though all of those feats are still useful to the light crossbow wielder (yes, even Crossbow Mastery). This combination will give you a range of 120', 1d10 damage, 19-20/x2 crit, Rapid Reload allows you to reload the clip in your HRC as a move action -- reload and fire in the same round, PBS adds +1 to attack /damage rolls within 30', Rapid Shot gives you an extra shot per round at your full BAB but incurs a -2 penalty to all attack rolls when you use it, and Crossbow Mastery allows you to reload ALL CROSSBOWS (repeating or otherwise) as a free action AND reloading the crossbow you chose for your RR feat does not incur an attack of opportunity.
Whichever way you go, take Rapid Reload FIRST. For the Light Crossbow, it's pretty obvious (no delay in attacks due to reload). For the HRC it's still very valuable, as you only get a single attack/round until you hit 8th level (unless you take Rapid Shot before then). Since you get 1 feat every odd level (and an extra at 1st if you're human), this gives you a total of 4 or 5 feats before you get that second attack. If you take them in this order: Rapid Reload, Point Blank Shot, Rapid Shot, and Crossbow Mastery, then you will be fully prepared for additional attacks before you get that second attack (excluding the extra from Rapid Shot). As a Human, by 5th level you'll have Crossbow Mastery and will never be delayed in your number of attacks due to reload time, and you'll be able to make full use of that Rapid Shot feat with no hickups.
All of this works with the regular Heavy Crossbow, as well, but your rapid shot feat will be wasted for 2 levels while you're waiting to get Crossbow Mastery, because reloading a Heavy Crossbow with Rapid Reload is still a Move Action.
And remember, once you have Crossbow Mastery, you can pick up ANY CROSSBOW and reload it as a free action, gaining your full compliment of attacks and reaping all the benefits of these feats. The only thing that blows is Crossbow Mastery completely overrides Rapid Reload, so now it feels like RR is a wasted feat, even though it is a prerequisite. It's best to try not to think about that. ;)
So, if you just want to be able to fire without skipping a beat, but aren't really worried about dealing damage (and there are plenty of other feats you can take, as well, though none are crossbow specific), then just go with the first option. If your intent is to be a secondary damage dealer, go with the second option. If you aren't sure, go with the first option and see how it feels. If you find you want more from your crossbow, remember that by the time you get to Crossbow Mastery, it will work for ALL crossbows... then start thinking about things like Deadly Aim (power attack for archery), Vital Strike (and Improved VS) (good for attacks on the move), and look into spells that buff archery or weapons.