Generally what the gentleman above me has said ^
If you have fast fingers and the enemy has a cc skill that may catch you out or change a teamfight e.g. amumu ult, sona ult, taric stun, etc then it will be a good idea to grab cleanse. If you do not have fast fingers or if they dont have cc then you can grab heal as an alternative to cleanse. Be warned though, many of the ad carry's (fotm like ezreal, corki , graves and others like missfortune) like to take ignite. This puts you in a difficult situation: if you use heal to try bait a kill, they may ignite you before you make your move and the heal will be reduced heavily. If you use it earlier before they ignite, they may just back off and you may have wasted your heal. As a result, you can turn to the all purpose ignite. This is great when you have a burst kill lane with alistar or taric but may make you feel alot squishier than others. It scales better early and falls off a little lategame unlike the others (heal scales best early to mid and cleanse is great all game through especially lategame).
TLDR: pick which according to the situation.